Endothelium-derived endothelin-1 reduces cerebral artery sensitivity to nitric oxide by a protein kinase C-independent pathway.
OBJECTIVE
Nitric oxide (NO) reduces endothelin-1 (ET-1) production and blunts ET-1 dependent vasoconstriction. The direct effects of smooth muscle ET(A) receptor stimulation on NO-mediated relaxation are unknown. We hypothesized that endothelium-derived ET-1 regulates vascular tone by reducing smooth muscle sensitivity to NO, possibly through activation of protein kinase C (PKC).


METHODS
Rings of rabbit middle cerebral artery were mounted on microvessel myographs to measure isometric tension. Dose-response curves to acetylcholine (ACh) and sodium nitroprusside (SNP; an NO donor) were obtained with or without ET-1 receptor blockade. Experiments were performed in the presence of indomethacin (10 micromol/L). Results are expressed as mean+/-SEM.


RESULTS
In depolarized conditions (40 mmol/L KCl physiological solution), ACh-induced relaxation was entirely NO-dependent, as indicated by its suppression by N(omega)-nitro-L-arginine (P<0.05). Arterial sensitivity (pD(2)) to ACh (6.32+/-0.11, n=6) was increased (P<0.05) to 6.77+/-0.10 (n=6) by BQ123 (ET(A) receptor antagonist, 5 micromol/L) but not by BQ788 (ET(B) receptor antagonist, 5 micromol/L; 6.08+/-0.22, n=5). Consistent with this finding, blockade of ET(A) receptors increased (P<0.05) vascular sensitivity to SNP (6.95+/-0.10, n=8), whereas BQ788 had no influence on arterial sensitivity to SNP (6.17+/-0.07, n=7) compared with control (6.43+/-0.13, n=11). In denuded arteries, the sensitivity to SNP (7.10+/-0.08, n=8) was reduced by exogenous ET-1 (6.51+/-0.35, n=7, P<0.05). Chelerythrine, a PKC inhibitor, did not alter smooth muscle sensitivity to NO, whereas phorbol 12-myristate 13-acetate, a PKC activator, strongly increased it.


CONCLUSIONS
Blockade of ET(A) but not ET(B) receptors sensitizes vascular smooth muscle to exogenous and endothelium-derived NO. This suggests that ET-1 regulates smooth muscle sensitivity to NO by a PKC-independent pathway. This represents an alternative pathway by which NO and ET-1 interact to regulate vascular tone.
Gilbert
P
P
Institut de cardiologie de Montréal, Montréal, Québec, Canada.
Tremblay
J
J
Thorin
E
E
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000096:biosynthesis* / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000378:metabolism*; D020536:Enzyme Activators / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D016166:Free Radical Scavengers / Q000494:pharmacology; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D020768:Middle Cerebral Artery / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism* / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011817:Rabbits; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology; D014666:Vasomotor System / Q000187:drug effects / Q000502:physiology
D000959:Antihypertensive Agents; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D014665:Vasodilator Agents; D009569:Nitric Oxide; D011493:Protein Kinase C; D007213:Indomethacin