Zhou, Z; Merkus, D; Cheng, C; Duckers, HJ; Danser, A; Duncker, DJ
Uridine adenosine tetraphosphate (Up4A) has been identified
as an endothelium-derived contracting factor, which acts through purinergic P2X and P2Y
receptors. Since the coronary vascular actions of Up4A are unknown, we investigated the
vasoactive profile of Up4A in coronary microvessels, and studied the involvement of purinergic
receptor subtypes. Studies were performed in isolated porcine coronary small arteries (diameter
similar to 250 mu m), with and without endothelial denudation, mounted on a Mulvany wire
myograph. Purinergic receptor expression was assessed by real-time PCR Up4A (10(-9)-10(-5) M)
failed to induce contraction at basal tone, but produced concentration-dependent vasorelaxation
in precontracted microvessels. Up4A was slightly less potent than adenosine, ATP, and ADP in
producing vasorelaxation, but significantly more potent than UTP and UDP. mRNA expression of P2X
(4), P2Y(1), P2Y(2), P2Y(4), P2Y(6) and A(2A), but not P2X(1), receptors was observed. Up4A-
induced vasodilation was unaffected by non-selective P2 receptor antagonist PPADS, P2X(1)
antagonist MRS2159, P2Y(1) antagonist MRS2179 and P2Y(6) antagonist MRS2578, but was markedly
attenuated by non-selective P1 receptor antagonist 8PT and A(2A) antagonist SCH58261. Up4A-
induced vasodilation was not affected by ectonucleotidase inhibitor ARL67156, suggesting that A
(2A) stimulation was not the result of Up4A breakdown to adenosine. Up4A-induced vasodilation was
blunted in denuded vessels; additional A(2A) receptor blockade further attenuated Up4A-induced
vasodilation, suggesting that A(2A) receptor-mediated vasodilation is only partly endothelium-
dependent. In conclusion, Up4A exerts a vasodilator rather than a vasoconstrictor influence in
coronary microvessels, which is mediated via A(2A) receptors and is partly endothelium-dependent.
(c) 2012 Elsevier Ltd. All rights reserved.
