Rapid Endothelial Cell–Selective Loading of Connexin 40 Antibody Blocks Endothelium-Derived Hyperpolarizing Factor Dilation in Rat Small Mesenteric Arteries

In resistance arteries, spread of hyperpolarization from the endothelium to the adjacent smooth muscle is suggested to be a crucial component of dilation resulting from endothelium-derived hyperpolarizing factor (EDHF). To probe the role of endothelial gap junctions in EDHF-mediated dilation, we developed a method, which was originally used to load membrane impermeant molecules into cells in culture, to load connexin (Cx)-specific inhibitory molecules rapidly (approximately 15 minutes) into endothelial cells within isolated, pressurized mesenteric arteries of the rat. Validation was achieved by luminally loading cell-impermeant fluorescent dyes selectively into virtually all the arterial endothelial cells, without affecting either tissue morphology or function. The endothelial monolayer served as an effective barrier, preventing macromolecules from entering the underlying smooth muscle cells. Using this technique, endothelial cell loading either with antibodies to the intracellular carboxyl-terminal region of Cx40 (residues 340 to 358) or mimetic peptide for the cytoplasmic loop (Cx40; residues 130 to 140) each markedly depressed EDHF-mediated dilation. In contrast, multiple antibodies directed against different intracellular regions of Cx37 and Cx43, and mimetic peptide for the intracellular loop region of Cx37, were each without effect. Furthermore, simultaneous intra- and extraluminal incubation of pressurized arteries with inhibitory peptides targeted against extracellular regions of endothelial cell Cxs (43Gap 26, 40Gap 27, and (37,43)Gap 27; 300 micromol/L each) for 2 hours also failed to modify the EDHF response. High-resolution immunohistochemistry localized Cx40 to the end of endothelial cell projections at myoendothelial gap junctions. These data directly demonstrate a critical role for Cx40 in EDHF-mediated dilation of rat mesenteric arteries.