Relative contributions of NO and gap junctional communication to endothelium-dependent relaxations of rabbit resistance arteries vary with vessel size

Two synthetic peptide inhibitors of gap junctional communication have been used to compare the contribution of direct cell-cell coupling to acetylcholine-induced relaxations of the rabbit central ear artery (G0) and its second branch generation (G2). These peptides, designated 43Gap 26 and 37,43Gap 27, possess sequence homology with specific domains of the first extracellular loop of connexin 43 (Cx43) and second extracellular loop of Cxs 37 and 43, respectively. Immunohistochemistry confirmed the presence of Cxs 37, 40, and 43 in the vascular endothelium, but of only Cx43 in the media of G0. At concentrations of 300 μM, 43Gap 26 and 37,43Gap 27 each inhibited the maximum response to acetylcholine in G2 by ∼50%, but by only ∼20% in G0, whereas inhibition of NO synthesis by 300 μM NG-nitro-L-arginine methyl ester attenuated maximum relaxations to acetylcholine by ∼30% in G2, but by ∼70% in G0. Residual endothelium-derived hyperpolanizing factor-type responses in G0 and G2 were abolished by 43Gap 26 and 37,43Gap 27. In HeLa cells transfected to express a chimeric Cx43-green fluorescent protein that forms functional gap junctions, the peptides were equally effective inhibitors of Lucifer yellow dye transfer. We conclude that the contribution of gap junctions to endothelium-dependent relaxation is inversely related to vessel size and exhibits an apparently reciprocal relationship with NO-mediated mechanisms of vasorelaxation in the rabbit ear.