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 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 were mediated via activation of P2X receptor. These
findings suggest that ATP-mediated contraction is not dependent on membrane
depolarization only, at least at low concentrations in the first order branches of chicken
anterior mesenteric artery. |
