Gating of connexin 43 gap junctions by a cytoplasmic loop calmodulin binding domain

Xu Q, Kopp RF, Chen Y, Yang JJ, Roe MW, Veenstra RD. Gating of connexin 43 gap junctions by a cytoplasmic loop calmodulin binding domain. Am J Physiol Cell Physiol 302: C1548-C1556, 2012. First published March 14, 2012; doi:10.1152/ajpcell.00319.2011.-Calmodulin (CaM) binding sites were recently identified on the cytoplasmic loop (CL) of at least three alpha-subfamily connexins (Cx43, Cx44, Cx50), while Cx40 does not have this putative CaM binding domain. The purpose of this study was to examine the functional relevance of the putative Cx43 CaM binding site on the Ca2+-dependent regulation of gap junction proteins formed by Cx43 and Cx40. Dual whole cell patch-clamp experiments were performed on stable murine Neuro-2a cells expressing Cx43 or Cx40. Addition of ionomycin to increase external Ca2+ influx reduced Cx43 gap junction conductance (G(j)) by 95%, while increasing cytosolic Ca2+ concentration threefold. By contrast, Cx40 G(j) declined by <20%. The Ca2+ -induced decline in Cx43 G(j) was prevented by pretreatment with calmidazolium or reversed by the addition of 10 mM EGTA to Ca2+-free extracellular solution, if Ca2+ chelation was commenced before complete uncoupling, after which g(j) was only 60% recoverable. The Cx43 CL136-158 mimetic peptide, but not the scrambled control peptide, or Ca2+/CaM-dependent kinase II 290-309 inhibitory peptide also prevented the Ca2+/CaM-dependent decline of Cx43 G(j). Cx43 gap junction channel open probability decreased to zero without reductions in the current amplitudes during external Ca2+/ionomycin perfusion. We conclude that Cx43 gap junctions are gated closed by a Ca2+/CaM-dependent mechanism involving the carboxyl-terminal quarter of the connexin CL domain. This study provides the first evidence of intrinsic differences in the Ca2+ regulatory properties of Cx43 and Cx40.