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Oscar A. Candia, Richard T. Mathias, Rosana Gerometta; Fluid Circulation Determined In The Isolated Bovine Lens. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1046.
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© ARVO (1962-2015); The Authors (2016-present)
The fluid circulation model (FCM) of Mathias et al. (1997)suggests that a circulation of Na within the lens draws a fluid flow capable of convecting essential nutrients into the deeper cortical and nuclear fibers. The FCM further proposes that Na and fluid entry into the polar regions are balanced by Na and fluid efflux at the lens equator, maintaining steady-state electrolyte levels and volume. Few studies have attempted to directly detect fluid transport by the lens, and antithetical results have been obtained (e.g. Fowlks, 1973; Fischbarg et al., 1999), contrary to our initial findings (ARVO 2003). We have now obtained additional data from recently performed experiments that corroborate, and substantiate, our earlier results.
Fresh bovine lenses (18 mm diameter) were isolated in a chamber with 3 compartments separated by 2 thin O-rings. Each compartment: anterior (An), equatorial (Eq) and posterior (Po) was connected to a vertical capillary graduated in µL. The chamber was kept at room temperature of 26±1°C. Since the total volume of the chamber was 5 mL, any putative 1-degree change represents 1.3 µL or ≈0.4 µL per capillary. The compartments were filled with Ringer’s so that the levels in the 3 capillaries were the same. Capillary levels were read every 15 min. If the sum of the levels varied more than 3 µL the experiment was discarded because it indicated either a leak, or an erroneous reading. The protocols consisted of a) 2 hrs in open circuit, b) 2 hrs in short circuit, c) 1 hr each open and short, and d) 1 hr each short and open.
In a total of 36 experiments the Eq capillary increased at an overall rate of 0.07 µl/min while the An and Po levels decreased at a rate of 0.05 and 0.03 µL/min, respectively. Thus, the outflow at the Eq was accounted for by the An and Po inflows that closed the circulating loop. The first hr flows under short circuit were about 30% larger than those in which the first hr was in open circuit conditions (p<0.005).
These experiments provide additional support that a fluid circulation consistent with the Mathias FCM is physiologically active. The effects of ion replacement are presented in a companion abstract.
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