Multiple connexins form gap junction channels in rat basilar artery smoothmuscle cells

Three connexins, Cx43, Cx40, and Cx37, have been found by protein or mRNA a nalysis to be prominent in mammalian blood vessels, but electrophysiologica l characterization of gap junction channels in freshly isolated vascular sm ooth muscle cells (SMCs) has not previously been reported. We used a dual-p erforated patch-clamp technique to study gap junction conductances in SMC p airs from rat basilar arteries. Macroscopic junctional conductance (G(j)) m easured in 98 cell pairs with either Cs+ or K+ ranged between 0.68 and 24.8 nS. In weakly coupled cells (G(j)<5 nS), single-channel currents were read ily resolved without pharmacological uncoupling agents, allowing identifica tion of 4 major unitary conductances. Two of these conductances, 80 to 120 pS and 150 to 200 pS, corresponded to the major conductance states for homo typic channels formed from Cx43 or Cx40, which we confirmed were present in smooth muscle by immunofluorescence analysis. Two other conductances, 220 to 280 pS and >300 pS, were identified that have not been previously report ed in vascular SMCs. Macroscopic recordings revealed currents that deactiva ted incompletely over a broad range of transjunctional potentials. In about half of the pairs, we identified macroscopic as well as single-channel cur rents that exhibited marked voltage asymmetry, consistent with nonhomotypic , ie, either heterotypic or heteromeric channels. Our data indicate that ba silar artery SMCs are coupled in vivo in a richly complex manner, involving Cx43, Cx40, and other large-conductance channels, and that a significant n umber of couplings involve putative nonhomotypic channels.