Is the chemical gate of connexins voltage sensitive? Behavior of Cx32 wild-type and mutant channels.
Connexin channels are gated by transjunctional voltage (Vj) or CO2 via distinct mechanisms. The cytoplasmic loop (CL) and arginines of a COOH-terminal domain (CT1) of connexin32 (Cx32) were shown to determine CO2 sensitivity, and a gating mechanism involving CL-CT1 association-dissociation was proposed. This study reports that Cx32 mutants, tandem, 5R/E, and 5R/N, designed to weaken CL-CT1 interactions, display atypical Vj and CO2 sensitivities when tested heterotypically with Cx32 wild-type channels in Xenopus oocytes. In tandems, two Cx32 monomers are linked NH2-to-COOH terminus. In 5R/E and 5R/N mutants, glutamates or asparagines replace CT1 arginines. On the basis of the intriguing sensitivity of the mutant-32 channel to Vj polarity, the existence of a "slow gate" distinct from the conventional Vj gate is proposed. To a lesser extent the slow gate manifests itself also in homotypic Cx32 channels. Mutant-32 channels are more CO2 sensitive than homotypic Cx32 channels, and CO2-induced chemical gating is reversed with relative depolarization of the mutant oocyte, suggesting Vj sensitivity of chemical gating. A hypothetical pore-plugging model involving an acidic cytosolic protein (possibly calmodulin) is discussed.
Peracchia
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Department of Pharmacology and Physiology, School of Medicine and Dentistry, University of Rochester, Rochester, New York 14642-8711, USA. cpera@pharmacol.rochester.edu
Wang
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Peracchia
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D000818:Animals; D002245:Carbon Dioxide / Q000502:physiology; D017630:Connexins / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology*; D004553:Electric Conductivity; D004563:Electrochemistry; D004594:Electrophysiology; D005260:Female; D017629:Gap Junctions / Q000502:physiology; D006706:Homeostasis / Q000502:physiology; D015640:Ion Channel Gating / Q000502:physiology*; D007473:Ion Channels / Q000235:genetics* / Q000378:metabolism*; D009154:Mutation / Q000502:physiology*; D012016:Reference Values; D014982:Xenopus laevis; D000097002:Gap Junction beta-1 Protein
D002245:Carbon Dioxide; D017630:Connexins; D007473:Ion Channels; D000097002:Gap Junction beta-1 Protein