Role of gap junctions in endothelium-derived hyperpolarizing factor responses and mechanisms of K+-relaxation

We have examined the effects of ouabain (1 mM), the gap junction inhibitors , 18 alpha-glycyrrhetinic acid (100 mu M), N-(piperidin-1-yl)-5-(4-chloroph enyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochlori de (SR141716A; 10 mu M) and palmitoleic acid (50 mu M), and clotrimazole (1 0 mu M) against endothelium-derived hyperpolarizing factor (EDHF)-mediated and K+-induced vasorelaxations in the rat mesentery. In the presence of ind omethacin (10 mu M) and 300-mu M N(G)nitro-L-arginine methyl ester (L-NAME) , carbachol caused EDHF-mediated relaxations (R-max = 85.3 +/- 4.0%). In th e presence of ouabain, these responses were substantially reduced (R-max = 11.0 +/- 2.3%). 18 alpha-glycyrrhetinic acid, SR141716A, palmitoleic acid a nd clotrimazole also significantly inhibited these EDHF-mediated responses. K+ caused vasorelaxation of preparations perfused with K+-free buffer (R-m ax = 73.7 +/- 2.4%), which were reduced by 10-mu M indomethacin (R-max = 56 .4 +/- 6.2%). K+ vasorelaxation was essentially abolished by endothelial de nudation. Both ouabain and 18 alpha-glycyrrhetinic acid opposed K+ relaxati ons, however, neither SR141716A, clotrimazole nor palmitoleic acid had any effect. Direct cell-cell coupling via gap junctions was attenuated by ouaba in, clotrimazole and palmitoleic acid. We conclude that: (i) that gap junct ional communication plays a major role in EDHF-mediated relaxations, (ii) t hat K+-vasorelaxation is endothelium-dependent (thus, K+ is unlikely to rep resent an EDHF), and (iii) that the inhibitory actions of ouabain and clotr imazole on gap junctions might contribute towards their effects against EDH F. (C) 2000 Elsevier Science B.V. All rights reserved.