Cyclic GMP-activated channels of rod photoreceptors show neither fast nor slow desensitization.
Desensitization of cGMP-activated channels was examined in excised, inside-out patches obtained from rod photoreceptors. Cyclic GMP was applied using a rapid-flow system in which concentration jumps are complete within 10-50 ms. In outer-segment patches containing many channels, the cGMP-dependent conductance reached a steady plateau that was maintained for tens of seconds in the presence of cGMP; thus, there was no indication of slow desensitization. However, rapid desensitization on the scale of milliseconds could not be ruled out because of limited speed of access of cGMP to the inner face of the patch membrane. To test for rapid desensitization, inner-segment patches containing only a single cGMP-activated channel were used. In these one-channel patches, there was no change in activity of the channel with time from its earliest onset after application of cGMP, indicating that rapid desensitization also did not occur.
Department of Neurobiology and Behavior, State University of New York, Stony Brook 11794-5230.
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Watanabe
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Matthews
D000818:Animals; D002024:Bufo marinus; D006152:Cyclic GMP / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D008027:Light; D008564:Membrane Potentials; D010786:Photoreceptor Cells / Q000378:metabolism / Q000502:physiology*
D007473:Ion Channels; D006152:Cyclic GMP