Effects of alpha,beta-methylene ATP on biphasic responses of rat vas deferens.

The epididymal region of isolated vas deferens of the rat was stimulated locally with field electrodes. Continuous perfusion with alpha,beta-methylene-adenosine-5'-triphosphate (mATP, 10(-5) M) desensitized the P2-purinoceptors and the effect of this on the two components of tetanic responses and the 'non-adrenergic' and adrenergic phases of single shock responses were examined. Exposure to mATP selectively prevented the contractions to adenosine-5'-triphosphate (ATP, 10(-4)-5 X 10(-4) M) but not noradrenaline (NA, 10(-5) M) and preferentially blocked the secondary but not the primary tetanic component. It also depressed markedly the non-adrenergic phase of single shocks and either reduced or abolished the adrenergic phase. Thus the secondary tension development depends in the rat vas deferens on both the activation of alpha 1-adrenoceptors and the non-adrenergic twitch mechanism. The action of mATP involves more processes than the desensitization of the P2-purinoceptors so does not positively identify purinergic transmission. Direct NA-induced contraction contributes more to the primary than to the secondary tetanic component.