Relaxation of rat thoracic aorta induced by the Ca(2+)-ATPase inhibitor, cyclopiazonic acid, possibly through nitric oxide formation.
1 The effect of the Ca(2+)-ATPase inhibitor, cyclopiazonic acid (CPA), was studied on rat thoracic aortic ring preparations. 2 At concentrations above 0.3 microM, CPA induced relaxation in the arteries precontracted with phenylephrine. Removal of the endothelium abolished CPA-induced relaxation. 3 The nitric oxide (NO) synthase inhibitor NG-nitro L-arginine (3-300 microM), the free radical scavenger haemoglobin (0.1-3 microM), the soluble guanylate cyclase inhibitor, LY83583 (0.1-10 microM), each inhibited the endothelium-dependent relaxation to CPA. The potassium channel blocker, glibenclamide (10 microM) and cyclo-oxygenase inhibitor, indomethacin (100 microM for 60 min and then washed out) did not alter the action of CPA. 4 The calmodulin inhibitors calmidazolium (3-10 microM) and W-7 (100 microM) also abolished CPA-induced relaxation. 5 CPA (10 microM) increased guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels in arteries with an intact endothelium, without affecting adenosine 3':5'-cyclic monophosphate (cyclic AMP) levels. 6 The inhibitors of NO synthesis and actions, the calmodulin inhibitor and removal of the endothelium abolished the CPA-stimulated increase in the levels of cyclic GMP. 7 In Ca(2+)-free solution, CPA failed to induce relaxation or to stimulate cyclic GMP production. Relaxation to nitroprusside was not affected under these conditions. 8 These results suggest that CPA can stimulate NO synthesis, possibly by inhibiting a Ca(2+)-ATPase, which replenishes Ca2+ in the intracellular storage sites in endothelial cells. Depletion of the Ca2+ store in the endothelium may then trigger influx of extracellular Ca2+, contributing to an increase in free Ca2+ in the endothelial cells, which activates NO synthase and NO formation.
Moritoki
H
H
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, University of Tokushima, Japan.
Hisayama
T
T
Takeuchi
S
S
Kondoh
W
W
Imagawa
M
M
D000594:Amino Acid Oxidoreductases / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D006152:Cyclic GMP / Q000096:biosynthesis; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D009569:Nitric Oxide / Q000096:biosynthesis* / Q000378:metabolism; D019001:Nitric Oxide Synthase; D019335:Nitroarginine; D051381:Rats; D017208:Rats, Wistar; D013268:Stimulation, Chemical
D000889:Anti-Arrhythmia Agents; D002147:Calmodulin; D007211:Indoles; D019335:Nitroarginine; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; D000252:Calcium-Transporting ATPases; D006152:Cyclic GMP; D002118:Calcium; C000543:cyclopiazonic acid