Mechanisms of Uridine Adenosine Tetraphosphate (Up4A)‐induced Contraction in Mice Aorta: Role of Thromboxane (TXA2) and Purinergic Receptors (P2R)

Abstract

Up4A, a novel endothelium‐derived vasoconstrictor, is proposed to play a role in cardiovascular disorders and induces aortic contraction through cyclooxygenases (COX). We demonstrated earlier that activation of A3 adenosine receptors (AR) results in aortic contraction via TXA2 production. However, the mechanisms of Up4A‐induced contraction are not understood. We hypothesize that Up4A‐induced contraction is via A3AR‐mediated TXA2 production. Concentration responses to Up4A were conducted in aorta from WT and A3AR KO. Up4A (10‐9‐10‐5 M) produced a dose‐dependent contraction (~80%), which was attenuated by non‐selective COX (indomethacin, 10 μM) and selective COX1 (SC560, 10 nM) but not by COX2 inhibition (NS398, 1 μM). Notably, Up4A‐induced contraction was blunted by TXA2 synthase inhibitor ozagrel (10 μM) and TXA2 receptor antagonist SQ29548 (1 μM). Non‐selective AR antagonist 8PST (100 μM) nor A3AR deletion affected Up4A‐induced contraction. However, both non‐selective P2R antagonist PPADS (10 μM) and P2X1R antagonist MRS2159 (30 μM) significantly attenuated Up4A‐induced contraction (~46% and 40%), respectively. Combination of ozagrel with MRS2159 further decreased this effect (~20%). Endothelial denudation almost fully reduced Up4A‐induced contraction. Furthermore, TXA2 production increased in vessels treated with Up4A (3 μM) (26.6±0.5 vs. 83.4±0.8 pg/mg), which was inhibited by either MRS2159 (49.0±0.7 pg/mg) or Ozagrel (42.4±0.5 pg/mg). In conclusion, Up4A‐induced contraction is via TXA2 production, which partially requires the activation of P2X1R but not A3AR through an endothelium‐dependent mechanism (Supported by HL 027339, HL 094447 and MEPSCKL201301).