Relationship between NaF- and thapsigargin-induced endothelium-dependent hyperpolarization in rat mesenteric artery.
1. In isolated rat mesenteric artery with endothelium, NaF caused slowly developing hyperpolarization. The hyperpolarizing effect was unchanged in the presence of N(G)-nitro-L-arginine (L-NOARG) and indomethacin, but was markedly reduced by high K+. In Ca2+ -free medium or in the presence of Ni2+, NaF failed to produce hyperpolarization. 2. NaF-induced hyperpolarization was substantially unaffected by deferoxamine, an Al3+ chelator, okadaic acid and calyculin A, phosphatase inhibitors, and preincubation with pertussis toxin, suggesting that neither the action of fluoroaluminates as a G protein activator nor inhibition of phosphatase activity contributes to the hyperpolarizing effect. 3. The selective inhibitors of the Ca2+ -pump ATPase of endoplasmic reticulum, thapsigargin and cyclopiazonic acid, elicited hyperpolarization, whose properties were very similar to those of NaF. When intracellular Ca2+ stores had been depleted with these inhibitors, NaF no longer generated hyperpolarization. 4. In Ca2+ -free medium, NaF (or thapsigargin) caused a transient increase in the cytosolic Ca2+ concentration ([Ca2+]i) in cultured porcine aortic endothelial cells, and subsequent application of thapsigargin (or NaF) failed to increase [Ca2+]i. 5. In arterial rings precontracted with phenylephrine, NaF produced endothelium-dependent relaxation followed by sustained contraction even in the presence of L-NOARG and indomethacin. The relaxant response was abolished by high K+ or cyclopiazonic acid. 6. These results indicate that NaF causes endothelium-dependent hyperpolarization, thereby leading to smooth muscle relaxation of rat mesenteric artery. This action appears to be mediated by the promotion of Ca2+ influx into endothelial cells that can be triggered by the emptying of intracellular Ca2+ stores, as proposed for those of thapsigargin and cyclopiazonic acid.
D000818:Animals; D001685:Biological Factors / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D004730:Endothelium, Vascular / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000502:physiology; D019335:Nitroarginine / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D012969:Sodium Fluoride / Q000494:pharmacology*; D019284:Thapsigargin / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects