The origin of the early receptor potential of the retina

Abstract

The early receptor potential of the isolated retina of the frog has the following properties It is unaffected by reversing the direction of incidence of the light, and by soaking the retina in isotonic solutions of salts containing neither sodium nor chloride. Soaking the retina in solutions containing high concentrations of salts or glycerol greatly alters its time course. Soaking the retina in solutions containing formaldehyde or N-ethyl maleimide slightly shortens its time course but does not otherwise much affect it. The authors argue that the early receptor potential depends on displacements of charge within the monolayers of visual pigment as they undergo a sequence of chemical changes after absorbing light. The time course of the observed response must differ from that of the movement of charge because of filtering by the resistance-capacity network in the receptors. Changes in the resistive components of this filter will partly or wholly account for the effects of salts and glycerol on the early receptor potential, but cannot explain those of temperature. It seems that at least two successive movements of charge must occur, the second of them strongly influenced by temperature. Neither movement requires the presence of free amino or thiol groups. The above hypothesis requires that all or most of the monolayers of visual pigment in a receptor be orientated the same way; they cannot face alternately in opposite directions.