The Early and Late Receptor Potentials of Monkey Cones and Rods

Abstract

A quantum of light, when absorbed by a molecule of visual pigment in the outer segment of a verte- brate photoreceptor, triggers a chain of events in the pigment molecule (Hubbard and Kropf, 1959; Wald et al., 1963). A series of rapid changes in molecular form precedes the slower splitting of the molecule into its chromophore and opsin fractions, and there has long been evidence that one of the rapid events triggers excitation of the photoreceptor (Hubbard and St. George, 1957; Wald et al, 1963). At the outset of the work reported here, however, no electrical activity had been demonstrated to occur in vertebrate photoreceptors. Thus it was necessary to detect and identify the electrical responses of these cells, in order to provide re- sponses by which the neurophysiology of vertebrate photoreceptors may be studied. It seemed of special importance that the electrical responses should fill the time scale...