Biochemical aspects of the visual process. XXV. Light-induced calcium movements in isolated frog rod outer segments

Suspensions of isolated rod outer segments are shown to have a high calcium content of up to 11 moles calcium per mole rhodopsin. Osmotic lysis of the outer segments demonstrates the presence of two calcium fractions, a soluble one and a particulate one. The particulate fraction apparently coincides with the rod disks or with disk fragments. Illumination of intact rod outer segments in calcium-free ATP-containing Ringer solution has no measurable effect upon their total caclium content, but causes a significant shift of calcium from the particulate to the soluble fraction. This light effect is retained in lysed outer segments resuspended in calcium-free ATP-containing Ringer. These results support a function of calcium as a transmitter in light transduction in rod outer segments.