Light adaptation and temperature effects in rat PIII retinal response: analysis with a two-state model.

Aspartate-isolated PIII responses from excised perfused retinas of albino rats were studied, with emphasis on background adaptation and temperature effects. When responses are measured at their peaks, it is seen that the proportion of response elicited by the background is equal to the proportion by which a test-flash response is suppressed. This supports the notion that rat PIII, although a complex response, seems to approximate a simple two-state ("compression") system and that it is therefore subject to analysis according to our recently proposed model. This model predicts that (i) responses from two-state systems should increase with decreasing temperature within limits; (ii) delta, the semisaturation constant of voltage--log intensity functions should shift to lower intensities with decreasing temperature; and (iii) the exact magnitude of the delta shift should follow the temperature dependence of the rate of rapid "neural" adaptation of the response. All of these predictions are verified for rat PIII. This suggests that rat PIII, although produced by at least two cell types, is being controlled by only two processes: a light-driven excitation and a rapid first-order "neural" dark adaptation.