The Effect of Calcium on Rat Lens Permeability.

In the absence of calcium, the penetration of sucrose and viannitol into the rat lens is increased, while that of inulin remains unchanged. The extracellular space of the lens, estimated with inulin, is 6 per cent of the wet iveight of the lens. The active accumulation of potassium and rubidium is 65 per cent of normal in the absence of calcium, while the uptake of a-aminoisobutyric acid (AIB) is only 20 per cent of normal. The loss of rubidium from the lens in the absence of calcium is considerably greater than that of AIB. The increased permeability of the lens shown with rubidium is sufficient to account for the change in concentration of potassium and sodium which takes place when the lens is incubated in calciumdeficient media. Sodium penetration into the lens is also calcium dependent, with the sodium Sjjace nearly equal to that of the lens water, in the absence of calcium.