Distinct Mechanisms Underlying α1-Adrenoceptor and P2x Purinoceptor Operated ATP Release and Contraction in the Guinea-Pig Vas Deferens

The temperature-dependence of ATP release and contraction response evoked by different agonists were investigated in superfused guinea-pig vas deferens. α-Adrenoceptor agonists, i.e. noradrenaline (300 μM), and α-methyl-noradrenaline (300 μM), increased the basal ATP outflow, measured by the luciferin-luciferase assay, and induced biphasic contractile response. Cooling the bath temperature to 12°C almost completely inhibited ATP release and twitch contraction evoked by α-adrenoceptor agonists, whereas the phasic contraction remained unaffected. In contrast, twitch contraction and subsequent ATP release induced by β,γ-methylene-ATP, a selective P2 receptor agonist (100 μM), was not reduced by low temperature. The ectoATPase activity, measured by HPLC technique was not significantly different at 37°C and 12°C. Nifedipine (1 μM), the voltage sensitive Ca2+ channel blocker eliminated β,γ-methylene-ATP evoked twitch contraction but not ATP release. In conclusion, α-adrenoceptor and P2 receptor agonists utilize distinct mechanisms to elicit ATP release and contraction: α-adrenoceptor-mediated ATP release and contraction is temperature-dependent, indicating the involvement of a carrier-mediated process in it, whereas P2x purinoceptor evoked ATP release and twitch is mediated by a different mechanism.