Slow bleach‐induced birefringence changes in rod outer segments.

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Abstract
Time resolved birefringence measurements revealed complex structural changes in [Rana pipiens] rod outer segments following a bleaching flash. The detailed character of the changes depended upon osmotic integrity of the outer segment envelope membrane. Rod outer segments with intact envelope membranes showed 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 was partially correlated with the formation of retinol. Rod outer segments with ruptured envelope membranes showed the initial and secondary losses, but the subsequent recovery only reached the dark-adapted level. Retinol did not form in such organelles. 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. Glycerol appeared to influence both the rate and magnitude of metarhodopsin III formtion, and of the spectrally silent secondary birefringence loss.