Characteristics of 45Ca uptake by the rabbit lens.

Lens 45Ca uptake was shown to increase when the external calcium concentration was less than 1 mM, suggesting that calcium ions themselves are able to interact with lens membranes in a way that influences the mechanism of calcium permeability. Strontium ions, added to a calcium-deficient bathing solution, were shown to attenuate the increased 45Ca uptake by the lens. There was no evidence for extracellular binding of calcium. Lens membrane permeability to calcium appeared not to be voltage-dependent since 45Ca uptake was not affected when the lens was depolarized by high potassium solutions. Calcium channel blockers were shown not to reduce the increased calcium leak resulting from exposure of the lens to a calcium-deficient medium.