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, an d it has been proposed that these may be due to the aforementioned dif ferences in age. We have tested this proposal by manipulating the rate s of renewal of the outer segments by exposing Xenopus laevis to diffe rent temperature and lighting regimes which are known to affect the ra tes of their outer segment membrane renewal. We have found that differ ences of responsiveness are, indeed, correlated with the differences i n the age gradients along the outer segments. (C) 1997 Elsevier Scienc e B.V.