Rod outer segment (ROS) renewal as a mechanism for adaptation to a new intensity environment. I. Rhodopsin levels and ROS length.

This study outlines the time course of cellular changes which occur within the renewal process of the rod cell during a switch to a new cyclic intensity environment. In the following experiments we demonstrate that by using the renewal process. Sprague-Dawley rats switched to a new cyclic intensity can adjust both the length of the outer segment and the amount of rhodopsin per retina. Previously it was established that the rod outer segment (ROS) length is not constant when animals are exposed to an intensity different from their normal environment. In the present study, we investigated how changes in ROS length were achieved by the rod cell. We noted that soon after a change in intensity, the ROSs were always shortened. This occurred when rats were switched either to a higher or lower light intensity than their rearing level. A final ROS length was achieved within 21 days (approximately two turnover periods). This length change required decreased disk removal in animals switched to a low light to achieve a lengthened ROS. In animals moved to a higher light intensity, however, disk removal rate did not change but ROS length did shorten, suggesting a change in disk addition. It is known that rhodopsin levels are up- and down-regulated with changes in environmental lighting. In this study, rhodopsin levels of animals switched from a low, cyclic intensity of 3 lx into a more intense cyclic light, 200 lx, dropped dramatically within 7 days to the rhodopsin value of an animal reared in the higher intensity.(ABSTRACT TRUNCATED AT 250 WORDS)