Combination of Ca2+ -activated K+ channel blockers inhibits acetylcholine-evoked nitric oxide release in rat superior mesenteric artery.
OBJECTIVE
The present study investigated whether calcium-activated K+ channels are involved in acetylcholine-evoked nitric oxide (NO) release and relaxation.


METHODS
Simultaneous measurements of NO concentration and relaxation were performed in rat superior mesenteric artery and endothelial cell membrane potential and intracellular calcium ([Ca2+]i) were measured.


RESULTS
A combination of apamin plus charybotoxin, which are, respectively, blockers of small-conductance and of intermediate- and large-conductance Ca2+ -activated K channels abolished acetylcholine (10 microM)-evoked hyperpolarization of endothelial cell membrane potential. Acetylcholine-evoked NO release was reduced by 68% in high K+ (80 mM) and by 85% in the presence of apamin plus charybdotoxin. In noradrenaline-contracted arteries, asymmetric dimethylarginine (ADMA), an inhibitor of NO synthase inhibited acetylcholine-evoked NO release and relaxation. However, only further addition of oxyhaemoglobin or apamin plus charybdotoxin eliminated the residual acetylcholine-evoked NO release and relaxation. Removal of extracellular calcium or an inhibitor of calcium influx channels, SKF96365, abolished acetylcholine-evoked increase in NO concentration and [Ca2+]i. Cyclopiazonic acid (CPA, 30 microM), an inhibitor of sarcoplasmic Ca2+ -ATPase, caused a sustained NO release in the presence, but only a transient increase in the absence, of extracellular calcium. Incubation with apamin and charybdotoxin did not change acetylcholine or CPA-induced increases in [Ca2+]i, but inhibited the sustained NO release induced by CPA.


CONCLUSIONS
Acetylcholine increases endothelial cell [Ca2+]i by release of stored calcium and calcium influx resulting in activation of apamin and charybdotoxin-sensitive K channels, hyperpolarization and release of NO in the rat superior mesenteric artery.
Stankevicius
E
E
Department of Pharmacology, Faculty of Health Sciences, University of Aarhus, Aarhus C, Denmark.
Lopez-Valverde
V
V
Rivera
L
L
Hughes
A D
AD
Mulvany
M J
MJ
Simonsen
Ulf
U
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D017609:Barium Compounds / Q000494:pharmacology; D001562:Benzimidazoles / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D018999:Charybdotoxin / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D017538:Mesenteric Artery, Superior / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism*; D010108:Oxyhemoglobins / Q000494:pharmacology; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology
D017609:Barium Compounds; D001562:Benzimidazoles; D002712:Chlorides; D007093:Imidazoles; D007211:Indoles; D010108:Oxyhemoglobins; D024681:Potassium Channels, Calcium-Activated; C110881:S-nitro-N-acetylpenicillamine; D014665:Vasodilator Agents; C487735:dimethylarginine; C024986:barium chloride; D018999:Charybdotoxin; D001030:Apamin; D009569:Nitric Oxide; D001120:Arginine; D010396:Penicillamine; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; C102635:1-ethyl-2-benzimidazolinone; D000109:Acetylcholine; D002118:Calcium; C000543:cyclopiazonic acid; D007213:Indomethacin