Selective inhibition of gap junction channel activity by synthetic peptides

1. The aim of this study was to inhibit specifically one type of gap juncti on channel in cells expressing multiple connexins (Cx) using synthetic olig opeptides. 2. A7r5 cells (an aortic smooth muscle cell line expressing Cx40 and Cx43) were incubated overnight with synthetic oligopeptides (P180-195) correspond ing to a segment of the second extracellular loop of Cx43. This segment is different in sequence from the corresponding location in Cx40. 3. P180-195 (500 mu M) decreased cell-to-cell coupling as assessed by dye c oupling and dual whole-cell voltage clamp. The decrease in permeability and junctional conductance was caused by selective inhibition of Cx43 gap junc tion channels. In contrast, overnight incubation of A7r5 cells with oligope ptides corresponding to a segment of the intracellular cytoplasmic tail of Cx43 was without effect. 4. These results indicate that oligopeptides P180-195 may interact with the extracellular domain of the Cx43 protein, thereby possibly mimicking conne xin-connexin binding. This apparently inhibits Cx43 channel activity withou t disturbing the activity of Cx40 channels. 5. Experiments with oligopeptides corresponding to the equivalent part of t he second extracellular loop of Cx40 (P177-192) pointed towards a selective inhibition of Cx40 channel activity. 6. Competition assays using synthetic oligopeptides may help to resolve the regulatory properties of gap junction channels in primary cells expressing multiple Cx.