title: Thapsigargin-induced endothelium-dependent triphasic regulation of vascular tone in the porcine renal artery.
abstract: 1. To elucidate the role of thapsigargin-induced Ca2+ entry in endothelial cells in the regulation of vascular tone, changes in Ca2+ and force of smooth muscle were simultaneously monitored in fura-2-loaded strips of porcine renal artery. 2. During phenylephrine-induced sustained contraction, thapsigargin caused an endothelium-dependent triphasic response; an initial relaxation, a subsequent transient contraction, and a sustained relaxation. The initial relaxation and the contraction were associated with a decrease and an increase in [Ca2+]i, respectively. There was no apparent [Ca2+]i decrease during the sustained relaxation. Thapsigargin-induced responses were observed at 10-8 M and higher concentrations, with the maximum response observed at 10-6 M. 3. The transient contraction was inhibited by a cyclo-oxygenase inhibitor (10-5 M indomethacin), a thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptor antagonist (10-5 M ONO-3708), and a TXA2 synthase inhibitor (10-5 M OKY-046). 4. During the phenylephrine-induced contraction in the presence of indomethacin, thapsigargin caused an initial, but not a sustained relaxation, in the presence of Nomega-nitro-L-arginine methylester (L-NAME). During the contraction induced by phenylephrine plus 40 mM K+-depolarization in the presence of indomethacin, thapsigargin induced both a transient and a sustained relaxation. However, these relaxations were completely abolished in the presence of L-NAME. 5. Thapsigargin caused a large Ca2+ elevation in cultured endothelial cells of the renal artery. The concentration-response relation was thus similar to that for force development in the arterial strips. 6. In conclusion, thapsigargin-induced Ca2+ entry in endothelial cells led to triphasic changes in the tone of the porcine renal artery. The endothelium-dependent contraction was mediated mainly by TXA2. Nitric oxide and hyperpolarizing factor are both involved in the initial relaxation. However, a sustained relaxation was observed which mainly depended on nitric oxide.
authors.affiliation: Division of Molecular Cardiology, Research Institute of Angiocardiology, Faculty of Medicine, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582 Japan.
authors.forename: E
authors.initials: E
authors.lastname: Ihara
authors.forename: K
authors.initials: K
authors.lastname: Hirano
authors.forename: J
authors.initials: J
authors.lastname: Nishimura
authors.forename: H
authors.initials: H
authors.lastname: Nawata
authors.forename: H
authors.initials: H
authors.lastname: Kanaide
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects*; D012077:Renal Artery / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D013552:Swine; D019284:Thapsigargin / Q000494:pharmacology*; D013930:Thromboxane-A Synthase / Q000037:antagonists & inhibitors
chemical_list: D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D019284:Thapsigargin; D013930:Thromboxane-A Synthase; D002118:Calcium