COMPARISON OF THE ACTIONS OF ATP AND UTP AT P-2X1 RECEPTORS IN SMOOTH-MUSCLE OF THE RAT TAIL ARTERY

The actions of ATP and uridine 5'-triphosphate (UTP) were compared at P-2X1 receptors in acutely dissociated smooth muscles cells of the rat tail artery. ATP (30 nM-100 mu M) and UTP (1 mu M-1 mM) elicited conc entration-dependent inward currents. ATP was approximately 100-fold mo re potent than UTP. In both cases, currents were activated within 3 ms of agonist application and had similar time-courses of activation and inactivation. The decay of responses for both agonists was concentrat ion-dependent and in most cells could be fitted by two exponentials. T he P-2X receptor antagonists suramin (100 mu M) and pyridoxalphosphate -6-azophenyl-2',4'-disulphonic acid (PPADS, 5 mu M) inhibited response s to both ATP and UTP. An action of UTP at P-2X1 receptors has not pre viously been reported. However, since the responses to ATP and UTP had similar time-courses and as PPADS and suramin inhibited both agonists , it is concluded that ATP and UTP are acting at the same site in thes e cells, the P-2X1 receptor. (C) 1998 Elsevier Science B.V. All rights reserved.