Abstract
Cyclic nucleotide-gated channels are nonselective cation channels activated by intracellular cAMP and/or cGMP. It is not known how the binding of agonists opens the channel, or how the presumed four binding sites, one on each subunit, interact to generate cooperativity. We expressed the rat olfactory cyclic nucleotide-gated channel α subunit in Xenopus oocytes and recorded the single-channel currents. The channel had a single conductance state, and flickers at −60 mV showed the same power spectrum for cAMP and cGMP. At steady state, the distribution patterns of open and closed times were relatively simple, containing one or two exponential components. The conductance properties and the dwell-time distributions were adequately described by models that invoke only one or two binding events to open the channel, followed by an additional binding event that prolongs the openings and helps to explain apparent cooperativity. In a comparison between cAMP and cGMP, we find that cGMP has clearly higher binding affinity than cAMP, but only modestly higher probability of inducing the conformational transition that opens the channel.
Footnotes
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Send reprint requests to: Dr. Henry A. Lester, Division of Biology 156-29, California Institute of Technology, Pasadena, CA 91125. E-mail: lester{at}caltech.edu
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↵1 Present address: Department of Genetics, Stanford University, 300 Pasteur Dr., M310, Stanford CA 94305
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This research was supported by a grant from the National Institutes of Health (NS-11756).
- Abbreviations:
- CNG
- cyclic nucleotide-gated
- rOCNC1
- rat olfactory channel, first subunit
- rOCNC2
- rat olfactory channel, second subunit
- Received September 24, 1998.
- Accepted January 28, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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