The light-suppressible K+ conductance and evaluation of internal messenger candidates in the molluscan extraocular photoreceptor.
A photoreceptor potential produced by a decrease in membrane conductance was not thought to occur in any invertebrate photoreceptors. However, we have found that the molluscan extraocular photoreceptor, A-P-1 responds to light with a depolarizing receptor potential due to a decrease in K+ conductance, so that the photoresponse associated with a decrease in membrane conductance is not unique to the vertebrate photoreceptor. The properties that the light-suppressible K+ conductance is time- and voltage-dependent are explained by comparison with those of the single channel conductance obtained in patch-clamp of both vertebrate and invertebrate photoreceptors. The noise analysis of the light-induced current suggest that this macroscopic light-suppressible conductance consists of channels. It is concluded that the light-suppressible K+ conductance is mediated by hydrolysis of cGMP which reduces internal cGMP, in agreement with the cGMP hypothesis of vertebrate phototransduction and that the hydrolysis may be modified by IP3.
Gotow
T
T
Department of Physiology, School of Medicine, Kagoshima University, Japan.
Nishi
T
T
Kijima
H
H
D000818:Animals; D008027:Light; D008974:Mollusca / Q000502:physiology*; D010786:Photoreceptor Cells / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*
D015221:Potassium Channels