Slow bleach-induced birefringence changes in rod outer segments.

1. Time resolved birefringence measurements reveal complex structural changes in rod outer segments following a bleaching flash. 2. The detailed character of the observed changes depends upon osmotic integrity of the outer segment envelope membrane. Rod outer segments with intact envelope membranes show a fast initial loss of intrinsic birefringence simultaneous with the formation of metarhodopsin II followed by a slower secondary loss. A subsequent birefringence increase to higher than the dark-adapted level is partially correlated with the formation of retinol. Rod outer segments with ruptured envelope membranes show the initial and secondary losses, but the subsequent recovery only reaches the dark-adapted level. Retinol does not form in such organelles. 3. The slow birefringence changes in intact rod outer segments were qualitatively different when Na+ salts were replaced by equimolar K+ salts in the bathing medium. 4. Glycerol appears to influence both the rate and magnitude of metarhodopsin III formation, and of the spectrally silent secondary birefringence loss.