Formation, conversion, and utilization of isorhodopsin, rhodopsin, and porphyropsin by rod photoreceptors in the Xenopus retina

Abstract

The visual pigment content of rod photoreceptors in Xenopus larvae was reduced >90% through a combination of vitamin A-deficient diet and constant light. Thereafter, a dose of either aU-trans-retinol or 9-cu-retinal was injected intramuscularly, leading to the formation of a rhodopsin (λmax 504 nm) or isorhodopsin (λmax 487-493 nm) pigment, respectively. Electrophysiological measurements were made of the threshold and spectral sensitivity of the aspartate- isolated Pill (photoreceptoral) component of the electroretinogram. These measures established that either rhodopsin or isorhodopsin subserved visual transduction with the same efficiency as the 519 nm porphyropsin pigment encountered normally. When animals with rhodopsin or isorhodopsin were kept in darkness or placed on a cyclical lighting regimen for 8 days, retinal densitometry showed that either pigment was being converted to porphyropsin; significantly more porphyropsin was formed as a result of cyclical lighting than after complete darkness. © 1978, Rockefeller University Press., All rights reserved.