Distinct mechanisms underlying alpha(1)-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 b y different agonists were investigated in superfused guinea-pig vas deferen s. alpha -Adrenoceptor agonists, i.e. noradrenaline (300 muM), and alpha -m ethyl-noradrenaline (300 muM), increased the basal ATP outflow, measured by the luciferin-luciferase assay, and induced biphasic contractile response. Cooling the bath temperature to 12 degreesC almost completely inhibited AT P release and twitch contraction evoked by alpha -adrenoceptor agonists, wh ereas the phasic contraction remained unaffected. In contrast, twitch contr action and subsequent ATP release induced by beta,gamma -methylene-ATP, a s elective P2 receptor agonist (100 muM), was not reduced by low temperature. The ectoATPase activity, measured by HPLC technique was not significantly different at 37 degreesC and 12 degreesC. Nifedipine (1 muM), the voltage s ensitive Ca2+ channel blocker eliminated beta,gamma -methylene-ATP evoked t witch contraction but not ATP release. In conclusion, alpha -adrenoceptor a nd P2 receptor agonists utilize distinct mechanisms to elicit ATP release a nd contraction: alpha -adrenoceptor-mediated ATP release and contraction is temperature-dependent, indicating the involvement of a carrier-mediated pr ocess in it, whereas P2x purinoceptor evoked ATP release and twitch is medi ated by a different mechanism.