Calcium accumulation in intracellular compartments of frog retinal rod photoreceptors.

The accumulation of calcium in the rod cells of isolated frog retinas was studied by methods involving the pretreatment of tissue with saponin, which reduces the permeability barrier posed by the plasma membrane, and the inclusion of a Ca2+ trapping agent, oxalate, in incubation media. X-ray microanalysis using an analytical transmission electron microscope was employed to verify the presence of calcium in the deposits produced by these methods. Ca2+ was found to accumulate in the rough endoplasmic reticulum (ER) and the agranular reticulum of the myoid region and in the presynaptic terminals of the rods. At least one aspect of this accumulation appears to depend upon the presence of ATP.