Light‐dependent subcellular movement of photoreceptor proteins

The intracellular localization of photoreceptor‐specific proteins 33 kd, beta‐transducin, and 48 kd, as determined by immunocytochemistry, is transient and dependent on the lighting environment to which the retina is exposed. Western analysis of the proteins in isolated rod outer segments from mouse retina demonstrates that beta‐transducin actually moves from the outer segment to the inner segement in response to light and that 48 kd moves simultaneously in the opposite direction. The light‐induced movements appear to be initiated by the absorption of light by rhodopsin because red light, which does not bleach rhodopsin, does not produce this redistribution of phototoreceptor proteins. Time course analysis of these movements suggests that the light‐induced shift is detectable at the earliest time examined (30 seconds). The bidirectional movement suggests that the photoreceptor cells have at least two distinct dyneinlike or kinesin‐like translocator molecules that act as microtubule‐based motors. This movement appears to be a basic mechanism by which photoreceptor cells rapidly and radically alter the subcellular concentrations of photoreceptor‐specific proteins, which in turn may affect the rapid changes in membrane potential that occur during phototransduction.