Li J, Lester H A
Division of Biology, California Institute of Technology, Pasadena, California 91125, USA.
Mol Pharmacol. 1999 May;55(5):883-93.
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 alpha 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.
环核苷酸门控通道是由细胞内cAMP和/或cGMP激活的非选择性阳离子通道。目前尚不清楚激动剂的结合如何打开通道，也不清楚假定的四个结合位点（每个亚基上一个）如何相互作用以产生协同性。我们在非洲爪蟾卵母细胞中表达了大鼠嗅觉环核苷酸门控通道α亚基，并记录了单通道电流。该通道具有单一的电导状态，在-60 mV时的闪烁显示cAMP和cGMP具有相同的功率谱。在稳态下，开放和关闭时间的分布模式相对简单，包含一或两个指数成分。仅通过一个或两个结合事件打开通道，随后通过一个额外的结合事件延长开放时间并有助于解释明显的协同性的模型，能够充分描述电导特性和驻留时间分布。在cAMP和cGMP的比较中，我们发现cGMP的结合亲和力明显高于cAMP，但诱导打开通道的构象转变的概率仅略高。
