Potential difference, resistance, cation content, and 86Rb efflux were measured in frog lenses maintained in normal or calcium-free EGTA Ringer's solution. Exposure of the lens to calcium-free solution resulted in a rapid fall in potential and resistance, together with a twofold increase in 86Rb efflux rate. These rapid changes were not due to an alteration in cation distribution between the lens and its environment. However, the alteration in 86Rb efflux rate could be explained on the basis of the fall in potential. These findings suggested that removal of calcium from the bathing medium caused a rapid increase in sodium permeability alone. This suggestion was substantiated by the results of experiments where the response of the lens to low calcium solution was determined in a medium in which 90% of the sodium had been replaced by sucrose.

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