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 microM), N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR141716A; 10 microM) and palmitoleic acid (50 microM), and clotrimazole (10 microM) against endothelium-derived hyperpolarizing factor (EDHF)-mediated and K(+)-induced vasorelaxations in the rat mesentery. In the presence of indomethacin (10 microM) and 300-microM N(G)nitro-L-arginine methyl ester (L-NAME), carbachol caused EDHF-mediated relaxations (R(max)=85.3+/-4.0%). In the presence of ouabain, these responses were substantially reduced (R(max)=11.0+/-2.3%). 18 alpha-glycyrrhetinic acid, SR141716A, palmitoleic acid and clotrimazole also significantly inhibited these EDHF-mediated responses. K(+) caused vasorelaxation of preparations perfused with K(+)-free buffer (R(max)=73.7+/-2.4%), which were reduced by 10-microM indomethacin (R(max)=56.4+/-6.2%). K(+) vasorelaxation was essentially abolished by endothelial denudation. Both ouabain and 18 alpha-glycyrrhetinic acid opposed K(+) relaxations, however, neither SR141716A, clotrimazole nor palmitoleic acid had any effect. Direct cell-cell coupling via gap junctions was attenuated by ouabain, clotrimazole and palmitoleic acid. We conclude that: (i) that gap junctional communication plays a major role in EDHF-mediated relaxations, (ii) that K(+)-vasorelaxation is endothelium-dependent (thus, K(+) is unlikely to represent an EDHF), and (iii) that the inhibitory actions of ouabain and clotrimazole on gap junctions might contribute towards their effects against EDHF.
Harris
D
D
School of Biomedical Sciences, E-Floor, University of Nottingham Medical School, Queen's Medical Centre, Nottingham NG7 2UH, UK.
Martin
P E
PE
Evans
W H
WH
Kendall
D A
DA
Griffith
T M
TM
Randall
M D
MD
D000818:Animals; D001464:Barium / Q000494:pharmacology; D001685:Biological Factors / Q000494:pharmacology*; D002217:Carbachol / Q000494:pharmacology; D002316:Cardiotonic Agents / Q000494:pharmacology; D004396:Coloring Agents; D004730:Endothelium, Vascular / Q000502:physiology; D017629:Gap Junctions / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D017538:Mesenteric Artery, Superior / Q000166:cytology / Q000187:drug effects*; D018721:Muscarinic Agonists / Q000494:pharmacology; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D001685:Biological Factors; D002316:Cardiotonic Agents; D004396:Coloring Agents; D018721:Muscarinic Agonists; C067410:endothelium-dependent hyperpolarization factor; D001464:Barium; D010042:Ouabain; D002217:Carbachol; D011188:Potassium