Endothelium‐dependent relaxation and endothelial hyperpolarization by P2Y receptor agonists in rat‐isolated mesenteric artery

Abstract

1 Vasorelaxation and hyperpolarization of endothelial cells by adenosine 5 0 -[b-thio]diphosphate (ADPbS) and adenosine 5 0 -[g-thio]triphosphate (ATPgS) were studied in rat-isolated mesenteric artery. Effects from stimulation of P2X receptors were avoided by desensitization with a,b-methylene adenosine triphosphate. 2 ADPbS caused concentration-and endothelium-dependent relaxations of methoxamineprecontracted small (third generation) and main mesenteric artery. These were inhibited by N o -nitro-L-arginine methyl ester (L-NAME) or a combination of apamin plus charybdotoxin (inhibitors of Ca 2+ -activated K + channels); L-NAME, apamin and charybdotoxin applied together abolished the response. 3 ATPgS induced limited relaxation (35% of methoxamine-induced tone at 10 mM) of small mesenteric artery, which was sensitive to L-NAME or endothelium denudation. However, it almost completely relaxed the main mesenteric artery over an extended concentration range (46 orders of magnitude) in an endothelium-dependent manner. This relaxation was inhibited by either L-NAME or a combination of apamin with charybdotoxin, and abolished by a combination of all the three inhibitors. 4 The P2Y 1 receptor antagonist MRS 2179 (2 0 -deoxy-N 6 -methyladenosine 3 0 ,5 0 -bisphosphate; 0.3 -3 mM) caused parallel rightward shifts of the concentration/relaxation curve to ADPbS (pA 2 ¼ 7.1). However, MRS 2179 did not inhibit, but potentiated, relaxant responses to ATPgS. MRS 2179 did not affect the contractile responses ATPgS in small mesenteric artery; ATPgS did not contract the main mesenteric artery. 5 ADPbS hyperpolarized the endothelium of the main mesenteric artery in a concentrationdependent manner. This was unaffected by L-NAME but antagonized by MRS 2179. ATPgS also hyperpolarized the mesenteric artery endothelium in a concentration-dependent manner but, when ATPgS was applied at 10 mM, its effect was potentiated by MRS 2179 (3 mM). 6 It is concluded that both relaxation and hyperpolarization to ADPbS are mediated by P2Y 1 receptors and that the endothelial hyperpolarization is related to the L-NAME-resistant relaxation. Relaxation to the P2Y 2 agonist ATPgS shows regional variation along the mesenteric vasculature. The mechanisms for potentiation of relaxation and hyperpolarization by ATPgS are unknown, but may indicate interactions between P2Y receptor subtypes.

Purinergic receptors in the splanchnic circulation

“…They observed that in rat mesenteric artery, relaxation of smooth muscle cells and hyperpolarization of endothelial cells caused by the P2Y 2 receptor agonist ATPγS were potentiated in the presence of MRS 2179, an antagonist of P2Y 1 receptors [105], as previously reported in non-splanchnic vessels [27,35,128].…”

“…Finally it may vary dramatically according to the vessel's internal diameter. P2Y 2 receptor-induced EDHF-mediated relaxation was clearly evident in large diameter main branch of the rat mesenteric artery (internal diameter of about 1.24 mm) but almost absent in the rat small mesenteric arteries (internal diameter of about 340 μm) [105]. In another study [172], electrical stimulation or adventitial application of ATP induced endothelium-dependent hyperpolarization in thin hamster mesenteric arteries (internal diameter < 150 μm) but not in thick arteries (internal diameter > 300 μm).…”

“…Furthermore, species differences may also account for the different profile of the two studies. Curiously, in arteries of about 350 μm, neither electrical stimulation or adventitial administration of ATP induced hyperpolarization [172] nor stimulation os P2Y 2 receptors with ATPγS caused vasodilation [105].…”

“…This vasodilation is probably mediated by P2Y 1 and P2Y 2 receptors, through hyperpolarization of the endothelium that correlates with endothelium-dependent vasodilation [105]. This P2Y receptor-induced endotheliummediated vasodilation occurs through the release of NO, via the NO/cGMP pathway [21], and cyclo-oxigenase metabolites [97,105] but also via the release of EDHF [97,98,99,105,148]. In fact, EDHF-mediated vasodilation seems to be the predominant mediator of P2 receptor-mediated regulation of perfusion pressure in the small arteries of the peripheral circulation [96,172].…”

Purinergic Component in the Coronary Vasodilatation to Acetylcholine after Ischemia-Reperfusion in Perfused Rat Hearts

“…This suggests that the relaxation in this condition may be mediated, at least in part, by activation of this subtype of purinergic receptors. It is known that purinergic P2Y receptors may produce vasodilatation in several vascular beds [26,27,28,29,30]. We do not know the endogenous mediator which activates these receptors in our experimental conditions, but it may be ATP.…”