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Combination of Ca 2+ ‐activated K + channel blockers inhibits acetylcholine‐evoked nitric oxide release in rat superior mesenteric artery
Author(s) -
Stankevičius E,
LopezValverde V,
Rivera L,
Hughes A D,
Mulvany M J,
Simonsen Ulf
Publication year - 2006
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0706886
Subject(s) - apamin , charybdotoxin , acetylcholine , chemistry , calcium , cyclopiazonic acid , medicine , endocrinology , hyperpolarization (physics) , biophysics , extracellular , membrane potential , intracellular , biochemistry , biology , stereochemistry , organic chemistry , nuclear magnetic resonance spectroscopy
Background and purpose: The present study investigated whether calcium‐activated K + channels are involved in acetylcholine‐evoked nitric oxide (NO) release and relaxation. Experimental approach: Simultaneous measurements of NO concentration and relaxation were performed in rat superior mesenteric artery and endothelial cell membrane potential and intracellular calcium ([Ca 2+ ] i ) were measured. Key results. A combination of apamin plus charybotoxin, which are, respectively, blockers of small‐conductance and of intermediate‐ and large‐conductance Ca 2+ ‐activated K channels abolished acetylcholine (10 μM)‐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 [Ca 2+ ] i . Cyclopiazonic acid (CPA, 30 μM), an inhibitor of sarcoplasmic Ca 2+ ‐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 [Ca 2+ ] i , but inhibited the sustained NO release induced by CPA. Conclusions and Implications: Acetylcholine increases endothelial cell [Ca 2+ ] 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. British Journal of Pharmacology (2006) 149 , 560–572. doi: 10.1038/sj.bjp.0706886