Effects of Ca2+ on the decay of rhodopsin photoproducts and photoreceptor adaptation in the isolated bullfrog retina.

Hanawa, Isao; Ando, Hiroshi; Matsuura, T.

doi:10.2170/jjphysiol.35.495

Cited by 1 publication

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“…Recently, ALBERT et al (1984) have suggested that rhodopsin stabilizes the bilayer structure of the disc membrane and Ca2+ destabilizes it. In addition, HANAWA et al (1985) demonstrated that the decay rate of rhodopsin intermediates increased by immersing the isolated retina in 0.01 mM Ca2+ solution. Considering the results mentioned, it appears likely that when photoreceptors are exposed to low levels of Ca2+ or papaverine, conformational changes of the disc membrane in the outer segment are produced by bleaching of rhodopsin, resulting in a decrease of the releasing rate of the internal transmitter from the disc.…”

Section: Discussionmentioning

confidence: 99%

Photoreceptor sensitivity as a function of rhodopsin content in the isolated bullfrog retina.

Toba

Hanawa

1985

Jpn.J.Physiol

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Using isolated bullfrog retina treated with both aspartate and Bat, the relation between the threshold of fast PIII response and rhodopsin content was examined. The change caused by a decrease in rhodopsin in response threshold from the original dark-adapted level could be described by the Michaelis-Menten equation. However, the data points deviated slightly from the theoretical curve when the rhodopsin content was below 30 %. After reducing Ca2+ concentration in the bathing solution from the normal (1.0 mM) to 0.01 mM, the threshold change of the response was more pronounced than that observed in the normal solution. In the presence of 0.1 mM papaverine, which is known as an inhibitor of phosphodiesterase, the threshold change increased in a similar way to that observed in 0.01 mM Ca2+ solution. However, isobutyl methylxanthine (IBMX), also an inhibitor of phosphodiesterase, showed no such effect. On the basis of the present findings, the transduction mechanism in the photoreceptors was discussed.Key words: bullfrog retina, photoreceptor, threshold, Ca2+, papaverine.Decrease in visual cell sensitivity during light adaptation depends on the amount of visual pigments bleached and their intermediates. The receptor sensitivity as a function of rhodopsin content was studied in isolated aspartate-treated retinas of the frog (MATSUURA, 1975; HAMILA, 1978, 1979) and the skate (PEPPERBERG et al., 1978). These studies demonstrated that the increase in log threshold was not linearly related to the rhodopsin concentration; bleaching of a small fraction of rhodopsin from the fully dark-adapted retina exerted a large effect on the threshold change.The PIYI response of an aspartate-treated retina, deprived of the pigment epithelium, consists of the fast (receptor potential) and the slow PIII responses.

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Section: Discussionmentioning

confidence: 99%