Gap junctional communication underpins EDHF-type relaxations evoked by AChin the rat hepatic artery

Synthetic peptides homologous to the Gap 26 and Gap 27 domains of the first and second extracellular loops of the major vascular connexins (Cx37, Cx40 , and Cx43) have been used to investigate the role of gap junctions in endo thelium-derived hyperpolarizing factor (EDHF)-type relaxations of the rat h epatic artery. These peptides were designated (37),(40)Gap 26, (43)Gap 26, (37),(43)Gap 27, and (40)Gap 27, according to connexin specificity. When ad ministered at 600 muM, none of the peptides individually affected maximal E DHF-type relaxations to ACh. By contrast, at 300 muM each, paired peptide c ombinations targeting more than one connexin subtype attenuated relaxation by up to 50%, and responses were abolished by the triple peptide combinatio n 43Gap 26 + (40)Gap 27 + (37),(43)Gap 27. In parallel experiments with A7r 5 cells expressing Cx40 and Cx43, neither (43)Gap 26 nor (40)Gap 27 affecte d intercellular diffusion of Lucifer yellow individually but, in combinatio n, significantly attenuated dye transfer. The findings confirm that functio nal cell-cell coupling may depend on more than one connexin subtype and dem onstrate that direct intercellular communication via gap junctions construc ted from Cx37, Cx40, and Cx43 underpins EDHF-type responses in the rat hepa tic artery.