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Rosana Gerometta, Oscar A. Candia; The Effects of Low Na and High K on Water Circulation of the Bovine Lens Isolated in a 3-Compartment Chamber. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1049.
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The fluid circulation model of Mathias et al. (1997) proposes that Na and fluid entry into the polar regions are balanced by Na and fluid efflux at the lens equator. In the absence of physiological levels of bath Na, lens circulating currents are gradually eliminated (Parmalee et al. 1986), as are hydrostatic pressure gradients within the lens (Gao et al. 2011). Thus, we investigated the effects of Na reduction in a chamber with which measurements of fluid circulation between poles and equator can be directly determined.
Fresh bovine lenses were isolated in a chamber with 3 compartments separated by 2 thin O-rings. Each compartment (filled with Ringer’s) was connected to a capillary, which was read every 15 min. Low Na solutions were prepared by replacing 110 mM NaCl in a standard Ringer’s solution with either N-methyl-D-glucamine (NMG)-HCl, or with KCl, thereby reducing bath Na from 145 to 35 mM. Our 2hr-protocols involved either: 2 hrs in low Na, or 1hr low Na-1 hr normal Ringer’s, or 1 hr normal Ringer’s-1 hr low Na. Either the NMG or the high K solutions were used for the low Na condition. The bathing solution for each condition was the same in the 3 bathing compartments.
In low Na (replaced by NMG), the flow was 0.014 μL/min in the first hr and was zero during the second hr. After the first hr in NMG solution with minimal flow, the water circulation remained inhibited when normal Ringer’s (NR) was used in the second hr. NMG inhibited the water flow observed in NR when used as replacement in the second hr. When high K (HK) was used as a partial replacement for Na, there was no inhibition of the water circulation, when used in the first or second hr before, or after, NR. There was no statistical difference between the NR and HK values in the first hr (0.034 μL/min) or second hr (0.014 μL/min). It was consistently observed that the values during the second hr were lower than those of the first hr independently of which solution was used in the first hr.
Unlike previous reports suggesting that Na reduction should inhibit water circulation, no influence was found when Na was reduced to 35 mM and replaced by K. If the replacement was NMG, an irreversible inhibition of the water flow was observed. Thus, the effect of Na replacement seems variable depending upon the type of lens and protocol utilized, suggesting that the mechanism by which ion transport drives water circulation is open to interpretation.
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