Dual regulation of cerebrovascular tone by UTP: P2U receptor-mediated contraction and endothelium-dependent relaxation.
1. The mechanisms of vascular tone regulation by extracellular uridine 5'-triphosphate (UTP) were investigated in bovine middle cerebral arterial strips. Changes in cytosolic Ca2+ concentration ([Ca2+]i) and force were simultaneously monitored by use of front-surface fluorometry of fura-2. 2. In the arterial strips without endothelium, UTP (0.1 microM-1 mM) induced contraction in a concentration-dependent manner. However, when the endothelium was kept intact, cumulative application of UTP (0.1-100 microM) (and only at 1 mM) induced a modest phasic contraction in arterial strips. This endothelium-dependent reduction of the UTP-induced contraction was abolished by 100 microM N omega-nitro-L-arginine (L-NOARG) but not by 10 microM indomethacin. In the presence of intact endothelium, UTP (30 microM) induced a transient relaxation of the strips precontracted with 30 nM U-46619 (a stable analogue of thromboxane A2), which was completely inhibited by pretreatment with L-NOARG but not with indomethacin. 3. In the endothelium-denuded strips, the contractile response to UTP was abolished by desensitization to either ATP gamma S or ATP (P2U receptor agonists), but not by desensitization to alpha, beta-methylene-ATP (P2x receptor agonist) or to 2-methylthio-ATP (P2Y receptor agonist). Desensitization to UTP abolished the contractile response to ATP. 4. In the endothelium-denuded artery, a single dose application of UTP induced an initial transient, and subsequently lower but sustained increase in [Ca2+]i and force. In the absence of extracellular Ca2+, UTP induced only the initial transient increases in [Ca2+]i and force, while the sustained increases in [Ca2+]i and force were abolished. UTP (1 mM) had no effect on the basic [Ca2+]i-force relationship obtained on cumulative application of extracellular Ca2+ at steady state of 118 mM K(+)-depolarization-induced contraction. 5. We conclude that in the presence of an intact endothelium, UTP-induced relaxation of preconstricted middle cerebral artery is mainly mediated indirectly, by the production of an endothelium-derived relaxing factor, but at high doses of UTP, vascular smooth muscle contraction is mediated directly via activation of P2U purinoceptor and [Ca2+]i elevation without Ca(2+)-sensitization of the contractile apparatus. UTP may thus exert a dual regulatory effect upon cerebrovascular tone, but in cases where the endothelium is impaired, it may also act as a significant vasoconstrictor.
Miyagi
Y
Y
Division of Molecular Cardiology, Research Institute of Angiocardiology, Fukuoka, Japan.
Kobayashi
S
S
Nishimura
J
J
Fukui
M
M
Kanaide
H
H
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002536:Cerebral Arteries / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000737:chemistry / Q000187:drug effects*; D019335:Nitroarginine / Q000494:pharmacology; D011450:Prostaglandin Endoperoxides, Synthetic / Q000037:antagonists & inhibitors; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000502:physiology*; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors; D014544:Uridine Triphosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D014662:Vasoconstrictor Agents / Q000037:antagonists & inhibitors
D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D011450:Prostaglandin Endoperoxides, Synthetic; D018048:Receptors, Purinergic P2; D014662:Vasoconstrictor Agents; D019335:Nitroarginine; D013928:Thromboxane A2; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D002118:Calcium; D014544:Uridine Triphosphate; D007213:Indomethacin