Gap junctions in vascular smooth muscle

Gap junction channels are the only class of channels which span two closely apposed plasma membranes. There are over a dozen identified subunit protei ns or connexins. Three generic types of gap junction channels are possible. They are the homotypic, heterotypic and heteromeric types, each of which h as a distinct connexin distribution. The major connexin found in vascular s mooth muscle is connexin43. Connexin40 has also been found in vascular smoo th muscle. The biosynthesis, trafficking and degradation of connexin43 has only recently been studied but the data reveal some interesting features su ch as a short half-life of only 1.5-3.5 h. The gating characteristics of co nnexin43 reveal mode shifting behaviours which result in prolonged closure of the majority of the gap junction channels. The channel also displays wea k voltage dependence and is poorly selective. These features suggest that d ynamical regulation of cell-to-cell coupling is best designed to reduce cel l-to-cell coupling, rather than enhance it, by down regulation of channel a ctivity through the biosynthesis, trafficking, degradation pathways and gat ing via mode shifting.