Activation of light-dependent K+ channels in ciliary invertebrate photoreceptors involves cGMP but not the IP3/Ca2+ cascade.
The activation of light-dependent K+ channels in ciliary photoreceptors from Pecten was investigated using intracellular dialysis of putative messengers and modulators. Neither elevated [Ca2+] nor BAPTA changed the membrane current in the dark or the light response. IP3 and the antagonists heparin and decavanadate were similarly ineffective, indicating that in these cells the IP3/Ca2+ signaling pathway is not crucial for phototransduction. By contrast, 8-Br-cGMP and cGMP induced an outward current accompanied by an increase in membrane conductance; 8-Br-cAMP was ineffective. The identity between the cGMP-induced and the light-induced currents is suggested by the following: both are carried by K+ and blocked by 4-AP, and both show outward rectification. In addition, guanine cyclic nucleotides depressed the photoresponse and induced single-channel currents in excised patches of light-sensitive membrane. These light-dependent channels therefore appear to represent a link between the families of cyclic nucleotide-gated channels and voltage-dependent K+ channels.
del Pilar Gomez
M
M
Department of Physiology, Boston University School of Medicine, Massachusetts 02118, USA.
Nasi
E
E
D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004553:Electric Conductivity; D006493:Heparin / Q000494:pharmacology; D007295:Inositol Phosphates / Q000378:metabolism / Q000494:pharmacology; D008027:Light; D008974:Mollusca; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D014638:Vanadates / Q000494:pharmacology
D007295:Inositol Phosphates; D015221:Potassium Channels; C016276:8-bromocyclic GMP; D014638:Vanadates; D004533:Egtazic Acid; D006493:Heparin; D015761:4-Aminopyridine; D006152:Cyclic GMP; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium