Mechanisms of the thapsigargin-induced Ca(2+) entry in in situ endothelial cells of the porcine aortic valve and the endothelium-dependent relaxation in the porcine coronary artery.
The mechanisms of the thapsigargin (TG)-induced capacitative Ca(2+) entry in in situ endothelial cells and its role in the regulation of arterial tone were investigated using front-surface fluorimetry and fura-2-loaded strips of porcine aortic valve and coronary artery. In the presence of extracellular Ca(2+), TG induced an initial rapid and a subsequent sustained elevation of cytosolic Ca(2+) concentration ([Ca(2+)](i)) in valvular strips. In the absence of extracellular Ca(2+), TG induced only a transient increase in [Ca(2+)](i). The TG-induced sustained elevation of [Ca(2+)](i) in endothelial cells was inhibited completely by 1 mM Ni(2+) and partly by 10 microM econazole and 30 microM ML-9, but not by 900 ng ml(-1) pertussis toxin or 100 microM wortmannin. Therefore, cytochrome P450 and protein phosphorylation are suggested to be involved in the TG-induced Ca(2+) influx in in situ endothelial cells. TG induced an endothelium-dependent large relaxation consisting of an initial and a late sustained relaxation in coronary arterial strip precontracted with U46619 (a thromboxane A2 analogue). Indomethacin alone had no effect, while indomethacin plus N(omega)-nitro-L-arginine (L-NOARG) markedly inhibited the sustained phase and slightly inhibited the initial phase of the TG-induced relaxation. TG induced a smaller but sustained relaxation during the 40 mM K(+)-induced precontraction than that seen during the U46619-induced precontraction. This relaxation was completely abolished by the pretreatment with indomethacin plus L-NOARG. In conclusion, both nitric oxide (NO) and endothelium-derived hyperpolarizing factor were suggested to mediate the TG-induced relaxation, while NO plays a major role in the sustained relaxation. The TG-induced sustained [Ca(2+)](i) elevation in endothelial cells was thus suggested to be mainly linked to the sustained production of NO.
Kuroiwa-Matsumoto
M
M
Department of Molecular Cardiology, Research Institute of Angiocardiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan.
Hirano
K
K
Ahmed
A
A
Kawasaki
J
J
Nishimura
J
J
Kanaide
H
H
D000818:Animals; D001021:Aortic Valve / Q000187:drug effects* / Q000378:metabolism; D001685:Biological Factors / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D003331:Coronary Vessels / Q000187:drug effects* / Q000502:physiology; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000502:physiology; D019335:Nitroarginine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D013552:Swine; D019284:Thapsigargin / Q000494:pharmacology*; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects*
D001685:Biological Factors; C067410:endothelium-dependent hyperpolarization factor; D019335:Nitroarginine; D009569:Nitric Oxide; D019284:Thapsigargin; D019001:Nitric Oxide Synthase; D011188:Potassium; D002118:Calcium