The Role of Metarhodopsin III in the Recovery of the PIII Photoresponse of Isolated Rat Retina after an Intense Light Exposure

Abstract

The PIII photoresponse of an isolated rat retina incubated in a calcium free medium and measured trans-retinally arises from the rods and possibly also from the Müller cells in close contact with them (Arden and Ernst, 1971; Faber, 1969). Immediately after an intense light exposure which decomposes a substantial proportion of rhodopsin in the receptors the maximum sized (i.e. “saturated”) PIII response that can be obtained to a brief test flash is very much reduced in amplitude. However, the amplitude grows in the following hour or so to the value it would have had, if the intervening light exposure had not occurred (Fig. 1). During this period slow thermal reactions can be followed in which the intermediate products of rhodopsin decomposition, metarhodopsin II and III (Meta II and III), decay to free opsin, retinal and retinol (Fig. 2), and we have been able to show that PIII recovery is linked with the formation of the final products (Fig. 3).