STUDIES ON MASS RECEPTOR POTENTIAL OF ISOLATED FROG RETINA .2. ON BASIS OF IONIC MECHANISM

The receptor potential of the excised frog retina was isolated by treatment of the tissue with Ringer solutions containing sodium aspartate, and was recorded by means of a pair of external electrodes on the opposite sides of the retina. Except at very low concentrations, the amplitude of the receptor potential varied in direct linear proportion to the logarithm of the external sodium concentration, and in inverse linear proportion to the logarithm of the external potassium concentration. The receptor potential could be generated by light even after the metabolic mechanism has been suppressed by ouabain, providing that a sodium concentration gradient was maintained. It was concluded that the primary action of light in generating the receptor potential is one of decreasing the permeability of the photoreceptor membrane to sodium. The metabolic pump is important only in maintaining the normal sodium concentration gradient. A model in the outer segment was proposed to explain the ionic mechanism in terms of the present and previous studies. © 1969.