The lens as an osmometer and the effects of medium osmolarity on water transport, 86Rb efflux and 86Rb transport by the lens

Abstract

The transport of water into or out of the lens was regulated by the osmotic gradients between lens and incubation media. Rabbit lenses incubated in hyposmotic Tyrode's media gained water while water losses were found in lenses in incubated in hyperosmotic Tyrode's media. Concomitant decreases or increases of intralenticular osmolarities to equilibrate the osmolarity of the bathing fluid were found in lenses incubated in the anisotonic media. The water gains or losses from lenses, induced by osmolarity changes, were reversible. Within the 238–368-mosM range of media osmolarities, the lens behaved as a “perfect osmometer”. Minimals lens swelling resulted in hydropic changes in lens epithelium cells and in lens fibers. Additional overhydration led to fluid collection in the interfibrillar space. The rate of 86Rb efflux from the lens increased in swollen lenses proportionally to the degree of hydration. The net transport of 86Rb into the lens was increased (+8, +18%) in minimally swollen lenses and markedly decreased (−50%) in lenses incubated in media −260 mosM hypotonic to the lens. The water permeability coefficient ( k) of lens was 0.4 μ·min −1·atm −1, a value smaller than the k of erythrocytes, of similar magnitude to the k of leukocytes and slightly higher than the k of marine invertebrate eggs.