Intercellular communication in cultured human vascular smooth muscle cells

Intercellular communication through gap junction channels plays a fundament al role in regulating vascular myocyte tone. We investigated gap junction c hannel expression and activity in myocytes from the physiologically distinc t vasculature of the human internal mammary artery (IMA, conduit vessel) an d saphenous vein (SV, capacitance vessel). Northern and Western blots docum ented the presence of connexin43 (Cx43) in frozen tissues and cultured cell s from both vessels. Northern blots also confirmed the presence of Cx40 mRN A in cultured IMA and SV myocytes. Dual whole cell patch-clamp experiments revealed that macroscopic junctional conductance was voltage dependent and characteristic of that observed for Cx43. In the majority of records, in bo th vessels, single-channel activity was dominated by a main-state conductan ce of 120 pS, with subconducting events comprising less than 10% of the amp litude histograms. However, some records showed "atypical" unitary events t hat had a conductance similar to Cx40 (similar to 140-160 pS), but gating b ehavior like that of Cx43. As such, it is conceivable that the presence and coexpression of Cx40 and Cx43 in IMA and SV myocytes may result in heterom eric channel formation. Nonetheless, in terms of gating, Cx43-like behavior clearly dominates.