Effects of light and temperature on the response gradient of retinal rod outer segments

Photoreceptor outer segments are continually renewed from base to tip and consequently the membrane at the tip is older than at the base. In parallel with this, there are differences in light responsiveness, and it has been proposed that these may be due to the aforementioned differences in age. We have tested this proposal by manipulating the rates of renewal of the outer segments by exposing Xenopus laevis to different temperature and lighting regimes which are known to affect the rates of their outer segment membrane renewal. We have found that differences of responsiveness are, indeed, correlated with the differences in the age gradients along the outer segments.