A New Property of the Early Receptor Potential of Rat Retina

Abstract

IN the dark-adapted eye, the amplitude of the early receptor potential (e.r.p.)¹ is linearly proportional to the number of molecules of rhodopsin bleached by a flash². The second of a train of intense flashes evokes a smaller response because less rhodopsin is available². However, with further stimulation, the e.r.p. reaches a steady voltage, about 10 per cent of the first response. This occurs even though each molecule of rhodopsin should, theoretically, have bleached many times over³. The relationship established by Cone² breaks down after the second or third maximal flash. The reason for this is that the flash causes regeneration of photopigment from a stable product of bleaching, by a mechanism different from that analysed by Williams³. The regeneration can be demonstrated by exposing the eye to a series of intense flashes (Fig. 1) until the e.r.p. amplitude has reached a stable lower level.