RELEASE OF ATP IN RAT VAS-DEFERENS - ORIGIN AND ROLE OF CALCIUM

Release of endogenous ATP elicited by electrical (neural) stimulation and exogenous agonists was studied in the rat isolated vas deferens. T he aims were to dissect neural and postjunctional contributions to the nerve activity-evoked overflow of ATP and to clarify the role of tran smitter receptors and calcium in postjunctional ATP release. In tissue s preincubated with [H-3]-noradrenaline, electrical stimulation (100 p ulses/10 Hz) elicited contraction and an overflow of tritium and ATP. Contractions as well as ATP overflow were reduced by prazosin 0.3 mu M and even more so by prazosin 0.3 mu M combined with suramin 300 mu M. They were also reduced by nifedipine 10 mu M and even more so by nife dipine 10 mu M combined with ryanodine 20 mu M (the additional effect of ryanodine on ATP overflow was not significant). In tissues not pret reated with [H-3]-noradrenaline, exogenous noradrenaline 10 mu M and a lpha,beta-methylene ATP 10 mu M elicited contraction and an overflow o f ATP. Responses to noradrenaline were blocked by prazosin 0.3 mu M bu t not suramin 300 mu M and were greatly reduced by nifedipine 10 mu M and in Ca2+-free medium. Responses to alpha,beta-methylene ATP were bl ocked by suramin 300 mu M but not prazosin 0.3 mu M, were reduced by n ifedipine 10 mu M (effect on ATP overflow not significant) and were re duced even more in Ca2+-free medium. Neuropeptide Y 0.3 mu M caused on ly very small contraction and ATP overflow. The electrically as well a s the agonist-evoked ATP overflow correlated well with the contraction responses except in experiments with suramin which retarded the remov al, by vas deferens tissue, of ATP from the medium. It is concluded th at the overflow of ATP from rat vas deferens elicited by electrical (n eural) stimulation is at least 90% postjunctional, presumably smooth m uscle, in origin. ATP is released from postjunctional cells as a conse quence of both alpha(1)-adrenoceptor and P-2-purinoceptor activation. Ca2+ is a second messenger in the postjunctional ATP release response; its major part enters through L-type channels. A ''purely neural'' ov erflow of ATP was not isolated under the conditions of the experiments .