The effect of ouabain on volume regulation in the rat lens

In an anisotonic medium the tendency of the lens to swell or shrink in response to the osmotic gradient is countered by a change in the content of lens solute, so that the change in the volume of lens water is minimal. This phenomenon is known as volume regulation. The rapid phase of volume regulation occurs in less than 1 hr and is followed by a slower phase that may require about 36 hr. In the present study the changes in the content of water, potassium and sodium were measured in the presence and absence of ouabain during 1 hr of incubation in anisotonic media. The effects of the ouabain-insensitive components of fluxes along electrochemical gradients are indicated by changes in the presence of ouabain, and the effects attributable to an active pump by the difference in changes in the presence and absence of ouabain. The results indicate that the volume of the lens after the initial phase of volume regulation is the same in the presence and absence of ouabain, that sodium influx varies with osmotic change, that the degree of sodium change cannot be accounted for by changes in the electrochemical driving force, that the sodium permeability is apparently decreased in hypotonic media and increased in an hypertonic medium, and that the changes in sodium influx can account for other changes associated with volume regulation.