May 2003
Volume 44, Issue 5
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Lens  |   May 2003
Influence of Age, Diabetes, and Cataract on Calcium, Lipid-Calcium, and Protein-Calcium Relationships in Human Lenses
Author Affiliations
  • Daxin Tang
    From the Departments of Ophthalmology and Visual Science and
  • Douglas Borchman
    From the Departments of Ophthalmology and Visual Science and
  • Marta C. Yappert
    Chemistry, University of Louisville, Louisville, Kentucky; the
  • Gijs F. J. M. Vrensen
    Lens and Cornea Research Unit, The Netherlands Ophthalmic Research Institute, Amsterdam, The Netherlands; and
  • Vittorio Rasi
    Udine, Italy.
Investigative Ophthalmology & Visual Science May 2003, Vol.44, 2059-2066. doi:10.1167/iovs.02-0345
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      Daxin Tang, Douglas Borchman, Marta C. Yappert, Gijs F. J. M. Vrensen, Vittorio Rasi; Influence of Age, Diabetes, and Cataract on Calcium, Lipid-Calcium, and Protein-Calcium Relationships in Human Lenses. Invest. Ophthalmol. Vis. Sci. 2003;44(5):2059-2066. doi: 10.1167/iovs.02-0345.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

purpose. Calcium is elevated in most cataractous human lenses and may contribute to cataractogenesis. In this study, age-related changes were examined in the total calcium content of clear human lenses and the binding of calcium to lens lipids and proteins.

methods. Total lens calcium was determined by atomic absorption spectroscopy. Calcium binding was measured by light scattering and measurement of calcium by atomic absorption spectroscopy in bound and unbound fractions.

results. The calcium content of clear human lenses decreased between 18 and 55 years of age and increased between 55 and 75 years, as well as in the presence of cataract. Total calcium levels in clear lenses from subjects with insulin-dependent diabetes did not differ from that in lenses of age-matched control subjects. In vitro binding studies have shown that lens lipids can bind nearly all the calcium present in the human lens. Age and cataract diminished the capacity of lens lipids to bind calcium. Calcium-induced light-scattering, measured in vitro for lens proteins, correlated with increasing age and cataract.

conclusions. The data support the hypothesis that increased intracellular calcium concentrations and a diminished capacity of lens lipids to bind to calcium initiate a cascade of events that culminates in increased light-scattering from lipids and especially proteins. Calcium binding to lipid membranes cannot directly contribute to light-scattering in cataractous lenses. It has been suggested that most of the diffusible calcium in the lens is in the intercellular spaces and that lens lipids in the outer leaflet of the bilayer bind to that calcium. If so, this could account for the 150-fold difference between free and bound calcium levels in the lens.

It has been almost a century since it was shown that calcium is elevated in cataractous lenses 1 and 75 years since total lens calcium was measured in clear lenses. 2 More recent work has confirmed a more than 23-fold increase in total lens calcium with cataract (Tables 1 2) . 1 2 3 4 5 6 7 8 9 Maintenance of calcium homeostasis is critical to the clarity of the lens. 12 13 14 The inward passive diffusion of calcium, perhaps through a nonspecific cation channel, 15 is countered by the actions of the plasma and sarco- and endoplasmic reticular Ca2+-adenosine triphosphatase (ATPase) pumps. 16 17 18 19 20 21 With age, the increased entry of calcium into clear lenses is offset by an increase in the activity of Ca2+-ATPase pumps. 22 With cataract, however, lens membrane permeability increases further, 23 24 25 26 total lens calcium is elevated, 1 2 3 4 5 6 7 8 9 and Ca2+-ATPase activity is decreased by 50%. 27 The Ca2+-ATPase pump is sensitive to lipid order, 28 29 which changes with age 29 and cataract. 27 31 32 Accordingly, the decrease of Ca2+-ATPase activity with cataract 27 may be a consequence of lipid structural changes, 27 31 32 an increase in Ca2+-ATPase oxidation, or both. 33 34 35  
Elevated calcium levels are related to numerous processes: activation of proteases, 36 37 inhibition of Na,K-ATPase activity, 38 39 cell growth, 40 protein synthesis, 41 disintegrative globulization, 42 calcium influx, 43 cell death, 44 increased membrane permeability, and aggregation of proteins 14 45 46 47 and lipids. 48 49 50 All these factors could contribute to alterations in lens molecular structure and increased light-scattering by the lens. Hightower and Reddy 7 showed that lens calcium content correlates with opacity in cataractous human lenses. 
As determined by electrodes, the total calcium concentration (Table 1) is approximately 150 times higher than that of free calcium in human lenses, 15 and it also is twice as high as the calcium concentration in the aqueous humor. 8 These differences suggest that calcium is sequestered in intracellular compartments or spaces, is bound to components of the lens, or both. Duncan and van Heyningen 6 noted that “elevated sodium could arise from Donnan forces alone, whereas elevated calcium must require the action of additional binding or complexing forces.” 
Intracellular compartments are present only in the outer cortical fibers of the lens. Accordingly, compartmentalization of calcium cannot account for the 150-fold difference between total calcium and free calcium in the cytoplasm of clear lenses. Furthermore, the nuclear region of the human lens, which has no organelles, contains twice as much calcium per dry weight as does the cortical region. 6  
β-Crystallin is not likely to bind calcium in the lens, because the dissociation constant (K d) of 0.38 mM 51 is several orders of magnitude higher than the free calcium concentration of the lens. 15 Calcium-binding proteins such as calmodulin have K d values in the lower 3-μM range. 52 53 54 Although these proteins can be expected to bind to calcium in the lens, they are present at an insufficient concentrations to account for the 100-fold difference between free and bound calcium. 
Calcium oxalate has been found in rare Morgagnian cataracts and in 39% of other cataracts. 55 56 57 However, calcium oxalate crystals have never been observed in clear lenses of individuals younger than 50 years 55 57 and therefore cannot account for the difference between free and bound calcium in clear, young lenses. 
An electron tomographic study has shown that a considerable amount of calcium in the human lens is located in intercellular spaces, where it is bound to the outer leaflet of the bilayer. 58 There is evidence that this is the case in rat lens as well. 59 It has been shown that calcium can bind to membranes composed of synthetic lipids, 48 50 thereby increasing light scattering. Membrane properties, such as permeability, membrane density, and hydration have been related to the intensity of light scattering from lipids. 60 61 These studies encouraged us to conduct this in vitro exploration of the relationships between light-scattering and calcium-lipid-binding in human lenses. We also measured age-related changes in the total lens calcium content of human lenses, which has not previously been studied by atomic absorption spectroscopy. 
Materials and Methods
Clear lenses were obtained from deceased human donors within 8 hours after death, from the Kentucky Lions Eye Bank (Louisville, KY) and the University of Kentucky Lions Eye Bank (Lexington, KY), and then frozen in liquid nitrogen. Clear lenses from eyes of donors who had been insulin-dependent for at least 5 years were noted. All human lenses were collected with informed consent. Bovine lenses were obtained from a slaughterhouse within 3 hours after the death of the animals. Reagents, bovine brain sphingomyelin, and α-crystallin were purchased from Sigma Chemical Co. (St. Louis, MO). With patients’ permission, an author (VR) collected cataractous lenses after performing extracapsular cataract extractions in Udine and Rome, Italy. All experiments were performed in accordance with the Declaration of Helsinki. 
Extraction of Human Lens Lipid
Lipid was extracted from human lenses by using a monophasic extraction protocol. 62 To remove oxygen, all solvents were bubbled with argon gas. The extraction was performed in an argon atmosphere. Glass centrifuge tubes were used throughout the extraction. Each pair of lenses was put in a glass centrifuge tube containing 10 mL of methanol. Lenses were cut with a metal spatula and sonicated with a microprobe sonicator (Branson; Ultrasonics Co., Danbury, CT) three to four times for 15 seconds, with a 30-second pause between sonication bursts to ensure that the samples were not heated. The solution was centrifuged at 5000 rpm for 1 hour and the supernatant decanted into another centrifuge tube, leaving a small amount of the upper layer to avoid disrupting the pellet. The methanol in the supernatant was evaporated with a rotary evaporator (Buchi Rotavapor 011; Brinkman Instruments, Inc., Westbury, NY). Hexane and isopropanol (2:1 vol/vol, 10 mL) were added to the dry lipid film and gently sonicated with a microprobe for 15 seconds. The solution was transferred to a centrifuge tube and centrifuged at 5000 rpm for 1 hour. The lipid-containing supernatant was decanted into another tube, taking care not to disturb the pellet, and the hexane and isopropanol were then evaporated with the rotary evaporator (Buchi Rotavapor 011; Brinkman Instruments, Inc.). 
Preparation of Large Unilamellar Vesicles of Human Lens Lipid
Human lens lipids (milligram range) dissolved in chloroform and methanol (7/3, vol/vol) were dried under nitrogen in glass test tubes, then lyophilized for 6 hours to remove remaining organic molecules. The dried lipid was suspended in 5 mM HEPES and 100 mM KCl buffer (pH 6.9). The dispersion was mixed with a vortex mixer (Scientific Industries Inc., Bohemia, NY) for 5 minutes at 45°C to make multilamellar vesicles. The vesicles were cooled to 4°C for 30 minutes and heated to 45°C for 30 minutes. We repeated the heating and cooling cycle three times to ensure that vesicles were completely formed. We prepared large unilamellar vesicles (LUVs) from the multilamellar vesicles at 45°C, using a lipid extruder (Lipex Biomembranes, Vancouver, British Columbia, Canada) and polycarbonate membranes (Whatman Nuclepore, Pleasanton, CA) according to the method of Hope et al. 63  
Measurement of Light-Scattering Intensity
Each sample contained 1.25 mg of LUVs in 1.5 mL 5 mM HEPES buffer and 100 mM KCl buffer (pH 6.9). To determine the effect of calcium on the light-scattering intensity of LUVs, we added 1.0 M CaCl2 stock solution to the LUV solution to give the appropriate final calcium concentration, ranging from 0 to 8 mM, and then incubated the samples for 16 hours. Light-scattering was measured with a photon-counting spectrofluorometer (PC1; ISS, Champaign, IL) at 90° with respect to the direction of the incident light. Radiation at 360 nm was used for excitation. During the measurement of light-scattering, samples were stirred with a magnetic stirrer. Data were averaged from at least 200 scans. 
Measurement of Calcium Binding
We measured light-scattering and then binding of calcium to lipid. After centrifuging the lipids at 150,000g for 1 hour, we decanted and diluted the supernatant and measured its calcium content by atomic absorption spectroscopy (Analyst 100 spectrometer; Perkin Elmer, Wellesley, MA). We compared the calcium content of the supernatant, representing unbound calcium, with the total calcium content of samples prepared in the same way but with no lipid. Bound calcium was calculated as the difference between the calcium content of samples containing lipid and those without lipid. The composition of bovine lens phospholipids was estimated from 31P-NMR and chemical composition studies. 64 We estimated that the average lipid molecular mass of bovine phospholipids and cholesterol is 575 g/mole. 
Measurement of Human Lens Calcium Content
For the determination of total calcium in pooled samples, we used six clear human lenses and eight human lenses with cataracts (four exclusively cortical and four with posterior subcapsular opacity). Lenses were fragmented with a metal spatula and sonicated with a microprobe sonicator (Branson; Ultrasonics Co.) in an argon-bubbled methanol solution. We evaporated the methanol solution under a stream of nitrogen gas and then lyophilized the samples for 16 hours to remove water and methanol. After weighing the samples, we added approximately 2 mL deionized water to each of them. Calcium content was measured by atomic absorption spectroscopy. 
To determine the total amount of calcium in individual lenses, we lyophilized lenses for 18 hours to remove all water and weighed them three times to 0.01 mg with a relative SD of 0.8%. Each lens was mixed with and brought to a volume of 10 mL with concentrated nitric acid containing 0.1% LaCl3 (7H2O). The lenses were sonicated in a bath-type sonicator (Model FS-9; Fisher Scientific, Pittsburgh, PA) for 45 minutes. Eighteen hours later, the lenses were completely solubilized. 
For atomic absorption spectroscopy, a 100-mM stock solution of CaCl2 was prepared by mixing CaCO3 with 75 mL of concentrated HCl. CaCO3 was used because it is not hydroscopic, as is CaCl2. Ten calcium standards ranging from 0.5 to 10 μΜ were prepared from the stock solution of calcium. Each standard solution contained 0.1% LaCl3 (H2O) and 10 mL concentrated nitric acid in a 200-mL volume. Standards were measured before and after samples, and samples were measured three times with a relative SD of 3.8%. 
Measurement of the Influence of Calcium on Light-Scattering by α-Crystallin
We used 11 samples, each containing 500 mg α-crystallin in 2 mL of 5 mM HEPES and 100 mM KCl buffer (pH 6.9). Calcium chloride stock solution was added to a final calcium concentration ranging from 0 to 220 mM. After 16 hours of incubation at 37°C, the light-scattering intensity was measured at 21°C. 
Measurement of the Effect of Calcium on the Protein of Young, Old, and Cataractous Lenses
Delipidated proteins were obtained from the pellets after lipid extraction. Each pellet was dried and weighed, then resuspended in 5 mM HEPES and 100 mM KCl buffer (pH 6.9). The resultant stock solution was stored at 4°C. Each protein stock solution was diluted to 1 mg protein in 2 mL HEPES buffer. The final calcium concentration was adjusted to 0, 2, 4, 5, and 6 mM with CaCl2. The protein suspension was incubated at 37°C for 16 hours under argon. Light-scattering intensities were measured at 21°C, as described earlier. 
Measurement of LUV Size
The size of lipid vesicles was estimated by cryoelectron microscope. We dipped bare grids into the samples, blotted them with filter paper, and vitrified the fluid film remaining on the grids in liquid ethane at −193°C. The samples were examined with the electron microscope at 100 kV and −174°C, in a vacuum of more than 10−8 mbar. For freeze-fracture microscopy, the samples were vitrified, fractured at a temperature of −120°C in a vacuum of more than 5 × 10−7 mbar, replicated with 2-nm Pt at an angle of 45°, and strengthened with 20-nm carbon. The replicas were cleansed with household bleach, rinsed with distilled water, and collected on bare 300-mesh grids. 
Results
The total calcium content decreased significantly (P = 0.003) in clear human lenses aged between 18 and 55 years. It then increased significantly (P =0.002) with age between 55 and 75 years (Fig. 1A) . The relative SD of total calcium in paired lenses from the same individual was 10%. 
The time between death and lens dissection, which ranged from 3 to 9 hours, did not influence the level of total calcium (Fig. 1B) . The average time of death to the time of lens dissection was similar in at all ages (Fig. 1C) . Total calcium increasedsignificantly with cataract. In clear lenses from eyes of insulin-dependent donors, total calcium levels did not significantly differ from the levels in age-matched control lenses (Fig. 2)
The equivalent of either two bovine brain sphingomyelin molecules or two bovine lens lipids (phospholipid and cholesterol) had the capacity to bind approximately one calcium molecule with half-maximal binding at 2.79 ± 0.02 mM (SEM; Fig. 3 ). 
Figure 4A shows a cryoscanning electron micrograph of human lens lipid LUVs. Two extrusions of the same lipid were made on different days. In young lenses (34 ± 16 years), the average diameter of LUVs was 260.8 ± 16 nm (n = 2568). Vesicle aggregation was evident after 1 hour of incubation with 1 mM free calcium (Fig. 4B)
With increasing age and cataract, the calcium-lipid-binding capacity (Fig. 5) and calcium-induced light-scattering (Fig. 6B) of human lens lipids decreased above a free calcium concentration of 2 mM. The level of half-maximum binding of calcium to lens lipids varied much more (2.6–5 mM) than that measured in bovine lens lipids or sphingomyelin (Fig. 3) . This is a consequence of the increase in the relative experimental error in assessing the 100-fold lower binding capacity of human lens lipids. 
Addition of 1 mM free calcium to LUVs from human lens lipids increased light-scattering in all 12 samples examined (Fig. 6A) . Calcium-induced light scattering for human lens proteins increased with increasing age and cataract (Fig. 6C) . Scattering from bovine lens α−crystallin also increased with increasing calcium content, reaching a maximum value near 60 mM of calcium (Fig. 6D) . A nonphysiological range of calcium was used to demonstrate that the K b for calcium binding to α−crystallin was above physiological levels (Fig. 6D) . Clear human lenses contained 6 mg/g phospholipid of lens tissue and 9.6 mg/g cholesterol of lens tissue. 62  
Discussion
Total Lens Calcium and Age
Relative to the dry weight of the lens, the total calcium in clear lenses decreased from 1.2 nanomoles/mg near the age of 20 years to 0.98 nanomoles/mg at 60 years of age, then increased to 2 nanomoles/mg near 75 years of age (Fig. 1A) . For total lens calcium to decrease between the ages of 20 and 60 years (Fig. 1A) , membrane permeability must decrease, Ca2+-ATPase activity must increase, or both must occur. Previous studies have shown that Ca2+-ATPase pump activity increases with age 22 and that there is little change in cation permeability between 20 and 60 years. 15 In clear human lenses, the increase in total calcium after 60 years of age (Fig. 1A) is a consequence of increased membrane permeability, 15 which begins after the age of 50 years and is not offset by an age-related increase in Ca2+-ATPase pump activity. 22 The levels of free calcium measured electrochemically in clear human lenses increased from approximately 10 μM in younger lenses to 12 to 20 μM in lenses of eyes from donors more than 50 years of age. 15 There was a similar increase in total calcium in lenses near 55 years of age (Fig. 1A)
In clear lenses, the nonlinear changes in total calcium (Fig. 1A) and free calcium 15 do not correlate with the linear increase in lens opacity observed with increasing age. 65 However, our data do not address possible changes in the regional distribution of calcium within clear lenses that could correlate with lens opacity. The data suggest that it is possible that as total calcium surpasses threshold value of 8 millimoles/kg lens water (Fig. 1A) , cataracts may develop (discussed in the next section). The level of 3.2 millimoles/kg total calcium of lens water is similar to the average value of 2.9 millimoles of total calcium per kilogram of lens water measured by others (Table 1)
Eckhert 66 noted a high degree of variability between individuals with respect to the number of cations in all eye tissues, reporting a relative SD of 43% among clear lenses of unreported ages. The large changes in calcium level with age (Fig. 1A) may have contributed to the variability in data in Eckhert, 66 as well as the wide range of total lens calcium content reported by many investigators (Table 1) . We found that the variation in total calcium within individuals (paired lenses) was only 10% compared with the 38% that Eckhert reported. 66  
Postmortem changes in calcium probably did not contribute to the changes we observed in total calcium with increasing age. As noted earlier, differences in time between death and lens dissection did not influence total calcium levels (Figs. 1B 1C) . That there was no change in the lens after death is not surprising, considering that the energy status and integrity of human lenses persist to 72 hours after death. Between 72 and 86 hours after death, the ATP/inorganic phosphate (Pi) ratio decreases by only 8%. 67 Furthermore, a decline in pH is not observed until 144 hours after death. 67  
Where Is the Calcium in Clear Lenses? Intracellular Compartmentalization, Calcium-Protein, Calcium-Oxalate, and Calcium-Lipid Binding
The total calcium concentration in the human lens (Table 1) is approximately 150 times higher than that of free calcium, as determined by electrodes, 15 and twice as high as the calcium concentration of the aqueous humor. 8 As discussed in the introduction, neither calcium bound to proteins, nor oxalate, nor calcium sequestered in intracellular compartments can account for the difference between bound and free calcium in the lens. Our data show that only at nonphysiological calcium concentrations did calcium bind to α-crystallin (Fig. 6D) , confirming that there is minimal binding of calcium to the crystallins in clear human lenses at the free calcium concentration of 20 μM. 51  
The present study also shows that lens lipids have a high capacity for binding calcium (Fig. 5) . Indeed, they can bind approximately 25 nanomoles of calcium, which represents between 40% and 100% of the total calcium reported in clear human lenses (Table 1) . Because the K b for calcium binding to lipids is 2.6 mM (Fig. 3) and because free intracellular calcium is in the micromolar range, little calcium is expected to bind to the lipids facing the cytoplasm. However, if most of the diffusible calcium is in the intercellular spaces, 58 59 68 and if these spaces are 15 nm wide 69 based on the relative area of the intracellular-to-intercellular space, we calculate the total amount of calcium in the intracellular spaces of a young lens would be 6 moles/kg of water. The lens lipids in the outer leaflet of the bilayer would bind to calcium at these concentrations. 
We found that the binding capacity of human lens lipids was approximately 100 times less than that of bovine lens lipids and bovine brain sphingomyelin (compare Figs. 3 and 5 ). Compositional differences account for these differences in binding. Regarding phospholipid content, the human lens contains approximately 3 times more cholesterol 64 70 than does the bovine lens. Our preliminary studies indicate that cholesterol greatly reduces the capacity of sphingomyelin membranes to bind calcium (Borchman D, unpublished results, 2000). In addition, the major lipid in the adult human lens is dihydrosphingomyelin (∼52%), whereas the bovine lens contains little dihydrosphingomyelin but, depending on the region, has a relatively large amount of sphingomyelin. 64 Molecular interactions may also explain the difference between the calcium-binding capacities of bovine and human lens lipids. Dihydrosphingolipids, which, as noted, are predominant in the human lens, pack together more strongly and more closely 71 than do sphingomyelin molecules. 72 As a consequence of their tighter packing, calcium appears to interact with sphingomyelin much more effectively than it does with dihydrosphingomyelin. 73  
Clear Lens Total Calcium and Diabetes
Calcium homeostasis was impaired in at least 15 tissues from humans with diabetes 74 and in lenses from diabetic rats 75 and rabbits. 76 Calcium-phosphate deposits have been identified in human lenses with diabetic cataracts. 77 Because of the link between diabetic cataracts and calcium, we examined clear lenses from donors who had been insulin-dependent for at least 5 years. The absence of any statistical difference between the total calcium of these lenses and those from age-matched control subjects (Fig. 2) indicates that factors other than elevated total calcium must contribute to the predisposition toward formation of cataract in those with diabetes. Our findings do not eliminate the possibility that changes in free calcium or alterations in the local distribution of total calcium contribute to diabetic cataracts. 
Lens Calcium and Cataract
We found that the total calcium in human lenses with cortical cataracts was four times higher than that in clear lenses (Table 2 ; Fig. 2 ). Our value of 12 millimoles calcium per kilogram of lens water is consistent with the values reported by three other investigators, which ranged from 4 to 65 millimoles calcium per kilogram of lens water (Table 2 ; Fig. 2 ). On the basis of the results in 10 studies that compared clear and cataractous lenses (Table 2) , it can be concluded that total calcium is elevated in almost all cataracts by an average of 2300%. Even pure nuclear cataracts have 2 to 26 times more total calcium than do clear lenses (Table 2) . The average level of 22 millimoles calcium per kilogram of lens water in cataractous lenses is remarkable (Table 2) . It is also 18 times higher than the amount of calcium in the aqueous humor. 8 The increase in total calcium with development of cataract cannot be attributed to lipid-calcium binding, because cataractous lens lipids have a diminished capacity to bind calcium (Fig. 5)
As total calcium in the lens increases, we hypothesize that higher intercellular calcium concentrations, coupled with decreased Ca2+-ATPase activity 27 and greater membrane permeability 15 22 23 24 25 26 could lead to elevated free intracellular calcium levels. This could, in turn, induce the formation of calcium oxylate crystals 55 56 and contribute to trigger a cascade of events that culminate in increased light-scattering from proteins (Fig. 6C) and, to a lesser extent, from lipids (Fig. 6B)
 
Table 1.
 
Calcium in Clear Lenses
Table 1.
 
Calcium in Clear Lenses
Age of Clear Lenses Total Calcium* (Free + Bound) Reference
23–66 y 287.5 Adams 2
30–72 y 8.1 Jedziniak 5
Not reported 5.6 Duncan and van Heyningen 6
Not reported 1.4 Hightower and Reddy 7
Not reported 0.83 Eckhert 66
67 y 0.7 Ringvold et al. 8
62.6 ± 4.5 y 0.55 Rasi et al. 4
65–75 y 2.4 Dilsiz et al. 9
8–75 y 3.2 Current study
Average excluding Adams data 2.9
Table 2.
 
Calcium in Cataractous Human Lenses
Table 2.
 
Calcium in Cataractous Human Lenses
Human Cataractous Lens Type Total Calcium* (Free + Bound) Total Calcium Cataract/Clear Reference
Mature (India) 58.0 NA Burge 1
Mature (USA) 118.0 NA Burge 1
Mature 76.0 2.7 Adams 2
Mature 40.0 5.1 Jedziniak 5
Mature 12.0 46.0 Hightower and Reddy 7
Mature 14.0 158.0 Ringvold et al 8
Mature 12.0 108.0 Rasi et al. 4
Mature 47.0 64.0 Average
Cortical 31.0 4.0 Jedziniak 5
Cortical 65.0 18.0 Duncan and Bushell 3
Cortical 12.0 6.9 Duncan and van Heyningen 6
Cortical 4.1 37.0 Rasi et al. 4
Cataract 12.0 3.8 Current study
Cortical 25.0 14.0 Average
Nuclear 3.6 1.0, † Duncan and Bushell 3
Nuclear 4.2 2.3 Duncan and van Heyningen 6
Nuclear 2.9 26.0 Rasi et al. 4
Nuclear 3.6 9.8 Average
Brown 29.0 3.9 Jedziniak 5
Brown India 4.7 17.0 Hightower and Reddy 7
Yellow 15.0 1.9 Jedziniak 5
Yellow 1.1 3.8 Hightower and Reddy 7
Colored 12.0 6.6 Average
Immature 0.4 1.5 Hightower and Reddy 7
Mixed cataract 2.2 20.0 Rasi et al. 4
Age onset 8.6 19.0 Dilsiz et al. 9
Immature 0.24 2.8 Ringvold et al. 8
Hypocalcemic 3.6 40.0 Ringvold et al. 8
Various 3.0 17.0 Average
All Types 22.0 23.0 Average
Figure 1.
 
(A) Total calcium in clear human lenses. Solid line: linear regression fit of data using a line order of 5. Dotted line: 95% confidence limits. Large open circles encompass overlapping data points. (B) Data correspond to lenses in (A). No postmortem-time-dependent changes in calcium were observed. Solid lines: linear regression fit of data using a line order of 1. (C) Data are for the lenses in (A). The time from death to dissection was not significantly different in the different age groups.
Figure 1.
 
(A) Total calcium in clear human lenses. Solid line: linear regression fit of data using a line order of 5. Dotted line: 95% confidence limits. Large open circles encompass overlapping data points. (B) Data correspond to lenses in (A). No postmortem-time-dependent changes in calcium were observed. Solid lines: linear regression fit of data using a line order of 1. (C) Data are for the lenses in (A). The time from death to dissection was not significantly different in the different age groups.
Figure 2.
 
Cataractous lenses were from a pool of lenses having four cortical and three posterior subcapsular cataracts, but no nuclear opacities. The control group of clear lenses was the same as that shown in Figure 1 . Donors had been insulin dependent for (at least) 5 years. Data are presented as average ± SEM in individual lenses, except for the cataractous lens data, in which ± represents the experimental deviation. Ten diabetic and 13 control lenses were examined.
Figure 2.
 
Cataractous lenses were from a pool of lenses having four cortical and three posterior subcapsular cataracts, but no nuclear opacities. The control group of clear lenses was the same as that shown in Figure 1 . Donors had been insulin dependent for (at least) 5 years. Data are presented as average ± SEM in individual lenses, except for the cataractous lens data, in which ± represents the experimental deviation. Ten diabetic and 13 control lenses were examined.
Figure 3.
 
Calcium binding to LUVs formed in extracted and extruded bovine lens lipids (○) and bovine brain sphingomyelin (•). The experiment was performed at 37.5°C. Data are expressed as ± SEM. An average molecular mass of 545 g/mol was used to calculate moles of bovine lens lipid.
Figure 3.
 
Calcium binding to LUVs formed in extracted and extruded bovine lens lipids (○) and bovine brain sphingomyelin (•). The experiment was performed at 37.5°C. Data are expressed as ± SEM. An average molecular mass of 545 g/mol was used to calculate moles of bovine lens lipid.
Figure 4.
 
Cryoelectron micrograph of LUVs extruded from older human lenses. (A) No calcium; (B) 1 hour of incubation with 1 mM free calcium at 36.5°C.
Figure 4.
 
Cryoelectron micrograph of LUVs extruded from older human lenses. (A) No calcium; (B) 1 hour of incubation with 1 mM free calcium at 36.5°C.
Figure 5.
 
Calcium-binding capacity in three pools of human lenses. A saturating calcium concentration of 6 mM was used. The average age of the young, older, and cataractous lens tissue is 30.3 ± 8.4, 75.6 ± 5.7, and 69.3 ± 8 years, respectively.
Figure 5.
 
Calcium-binding capacity in three pools of human lenses. A saturating calcium concentration of 6 mM was used. The average age of the young, older, and cataractous lens tissue is 30.3 ± 8.4, 75.6 ± 5.7, and 69.3 ± 8 years, respectively.
Figure 6.
 
Light-scattering (360 nm, 90°) at 36°C. (A) Change in intensity after adding 1 mM calcium to human lens lipid LUVs (B) bovine lens (▪) lipid LUVs; human lens (○) lipid LUVs. The average age of the younger, older, and cataractous pool of lens tissue is 30.3 ± 8.4, 75.6 ± 5.7, and 69.3 ± 8.5 years, respectively. (C) Human lens homogenates containing protein from the same three pools of human lenses used in Figures 1 and 4 . (D) Bovine lens α-crystallin.
Figure 6.
 
Light-scattering (360 nm, 90°) at 36°C. (A) Change in intensity after adding 1 mM calcium to human lens lipid LUVs (B) bovine lens (▪) lipid LUVs; human lens (○) lipid LUVs. The average age of the younger, older, and cataractous pool of lens tissue is 30.3 ± 8.4, 75.6 ± 5.7, and 69.3 ± 8.5 years, respectively. (C) Human lens homogenates containing protein from the same three pools of human lenses used in Figures 1 and 4 . (D) Bovine lens α-crystallin.
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Figure 1.
 
(A) Total calcium in clear human lenses. Solid line: linear regression fit of data using a line order of 5. Dotted line: 95% confidence limits. Large open circles encompass overlapping data points. (B) Data correspond to lenses in (A). No postmortem-time-dependent changes in calcium were observed. Solid lines: linear regression fit of data using a line order of 1. (C) Data are for the lenses in (A). The time from death to dissection was not significantly different in the different age groups.
Figure 1.
 
(A) Total calcium in clear human lenses. Solid line: linear regression fit of data using a line order of 5. Dotted line: 95% confidence limits. Large open circles encompass overlapping data points. (B) Data correspond to lenses in (A). No postmortem-time-dependent changes in calcium were observed. Solid lines: linear regression fit of data using a line order of 1. (C) Data are for the lenses in (A). The time from death to dissection was not significantly different in the different age groups.
Figure 2.
 
Cataractous lenses were from a pool of lenses having four cortical and three posterior subcapsular cataracts, but no nuclear opacities. The control group of clear lenses was the same as that shown in Figure 1 . Donors had been insulin dependent for (at least) 5 years. Data are presented as average ± SEM in individual lenses, except for the cataractous lens data, in which ± represents the experimental deviation. Ten diabetic and 13 control lenses were examined.
Figure 2.
 
Cataractous lenses were from a pool of lenses having four cortical and three posterior subcapsular cataracts, but no nuclear opacities. The control group of clear lenses was the same as that shown in Figure 1 . Donors had been insulin dependent for (at least) 5 years. Data are presented as average ± SEM in individual lenses, except for the cataractous lens data, in which ± represents the experimental deviation. Ten diabetic and 13 control lenses were examined.
Figure 3.
 
Calcium binding to LUVs formed in extracted and extruded bovine lens lipids (○) and bovine brain sphingomyelin (•). The experiment was performed at 37.5°C. Data are expressed as ± SEM. An average molecular mass of 545 g/mol was used to calculate moles of bovine lens lipid.
Figure 3.
 
Calcium binding to LUVs formed in extracted and extruded bovine lens lipids (○) and bovine brain sphingomyelin (•). The experiment was performed at 37.5°C. Data are expressed as ± SEM. An average molecular mass of 545 g/mol was used to calculate moles of bovine lens lipid.
Figure 4.
 
Cryoelectron micrograph of LUVs extruded from older human lenses. (A) No calcium; (B) 1 hour of incubation with 1 mM free calcium at 36.5°C.
Figure 4.
 
Cryoelectron micrograph of LUVs extruded from older human lenses. (A) No calcium; (B) 1 hour of incubation with 1 mM free calcium at 36.5°C.
Figure 5.
 
Calcium-binding capacity in three pools of human lenses. A saturating calcium concentration of 6 mM was used. The average age of the young, older, and cataractous lens tissue is 30.3 ± 8.4, 75.6 ± 5.7, and 69.3 ± 8 years, respectively.
Figure 5.
 
Calcium-binding capacity in three pools of human lenses. A saturating calcium concentration of 6 mM was used. The average age of the young, older, and cataractous lens tissue is 30.3 ± 8.4, 75.6 ± 5.7, and 69.3 ± 8 years, respectively.
Figure 6.
 
Light-scattering (360 nm, 90°) at 36°C. (A) Change in intensity after adding 1 mM calcium to human lens lipid LUVs (B) bovine lens (▪) lipid LUVs; human lens (○) lipid LUVs. The average age of the younger, older, and cataractous pool of lens tissue is 30.3 ± 8.4, 75.6 ± 5.7, and 69.3 ± 8.5 years, respectively. (C) Human lens homogenates containing protein from the same three pools of human lenses used in Figures 1 and 4 . (D) Bovine lens α-crystallin.
Figure 6.
 
Light-scattering (360 nm, 90°) at 36°C. (A) Change in intensity after adding 1 mM calcium to human lens lipid LUVs (B) bovine lens (▪) lipid LUVs; human lens (○) lipid LUVs. The average age of the younger, older, and cataractous pool of lens tissue is 30.3 ± 8.4, 75.6 ± 5.7, and 69.3 ± 8.5 years, respectively. (C) Human lens homogenates containing protein from the same three pools of human lenses used in Figures 1 and 4 . (D) Bovine lens α-crystallin.
Table 1.
 
Calcium in Clear Lenses
Table 1.
 
Calcium in Clear Lenses
Age of Clear Lenses Total Calcium* (Free + Bound) Reference
23–66 y 287.5 Adams 2
30–72 y 8.1 Jedziniak 5
Not reported 5.6 Duncan and van Heyningen 6
Not reported 1.4 Hightower and Reddy 7
Not reported 0.83 Eckhert 66
67 y 0.7 Ringvold et al. 8
62.6 ± 4.5 y 0.55 Rasi et al. 4
65–75 y 2.4 Dilsiz et al. 9
8–75 y 3.2 Current study
Average excluding Adams data 2.9
Table 2.
 
Calcium in Cataractous Human Lenses
Table 2.
 
Calcium in Cataractous Human Lenses
Human Cataractous Lens Type Total Calcium* (Free + Bound) Total Calcium Cataract/Clear Reference
Mature (India) 58.0 NA Burge 1
Mature (USA) 118.0 NA Burge 1
Mature 76.0 2.7 Adams 2
Mature 40.0 5.1 Jedziniak 5
Mature 12.0 46.0 Hightower and Reddy 7
Mature 14.0 158.0 Ringvold et al 8
Mature 12.0 108.0 Rasi et al. 4
Mature 47.0 64.0 Average
Cortical 31.0 4.0 Jedziniak 5
Cortical 65.0 18.0 Duncan and Bushell 3
Cortical 12.0 6.9 Duncan and van Heyningen 6
Cortical 4.1 37.0 Rasi et al. 4
Cataract 12.0 3.8 Current study
Cortical 25.0 14.0 Average
Nuclear 3.6 1.0, † Duncan and Bushell 3
Nuclear 4.2 2.3 Duncan and van Heyningen 6
Nuclear 2.9 26.0 Rasi et al. 4
Nuclear 3.6 9.8 Average
Brown 29.0 3.9 Jedziniak 5
Brown India 4.7 17.0 Hightower and Reddy 7
Yellow 15.0 1.9 Jedziniak 5
Yellow 1.1 3.8 Hightower and Reddy 7
Colored 12.0 6.6 Average
Immature 0.4 1.5 Hightower and Reddy 7
Mixed cataract 2.2 20.0 Rasi et al. 4
Age onset 8.6 19.0 Dilsiz et al. 9
Immature 0.24 2.8 Ringvold et al. 8
Hypocalcemic 3.6 40.0 Ringvold et al. 8
Various 3.0 17.0 Average
All Types 22.0 23.0 Average
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