The relationship between ATP-induced membrane potential and contraction was investigated in the smooth muscle of chicken anterior mesenteric artery using microelectrode and tension recording techniques, respectively. Application of ATP to endothelium-denuded arterial preparations developed concentration-dependent, slow depolarization which started only at concentrations not less than 10 μM. On the other hand the tension recording experiment revealed that ATP produced concentration-dependent contractions, which were evident at concentrations lower than those evoked depolarizing response to ATP (as lower as 100 nM). Both depolarizing & contracting responses were abolished by the P2X receptor blocker, PPADS (50 μM) but not by P2Y receptor blocker CBF3GA (100 μM); indicating that the excitatory responses of ATP are mediated via activation of P2X receptor. These findings show that ATP-mediated contraction is not dependent on membrane depolarization, at least at low concentration in the first order branches of chicken anterior mesenteric artery. |
