Characterization of Gap Junction Channels in A7r5 Vascular Smooth Muscle Cells

Recent evidence suggest that coordination of blood flow in the microcirculation involves cell-to-cell coupling via gap junctions. In this study, using A7r5 cells as a model of vascular smooth muscle, we have characterized the gap junctions in terms of the unitary conductances of the observed channels, the responses to second messengers, and subunit protein composition. The cells were typically well coupled several hours after plating, with junctional conductances on the order 20-40 nS. Channels with mean conductances of 36 and 89 pS were observed in low-conductance cell pairs and in cell pairs whose macroscopic conductance was reduced by exposure to halothane. Connexin43 was the only known gap junction sequence detected by Northern blots (low and high stringency), immunoblots, or immunohistochemical studies. Junctional conductance was reduced 15% by 8-bromoadenosine 3',5'-cyclic monophosphate; 8-bromoguanosine 3',5'-cyclic monophosphate had no effect. The results suggest that connexin43 can form stable channels of at least two distinct conductances and gap junctions with differing responses to second messengers.