Inhibition of excitatory junction potentials in guinea-pig vas deferens by alpha, beta-methylene-ATP: further evidence for ATP and noradrenaline as cotransmitters

Abstract

Excitatory junction potentials (e.j.p.s) and spontaneous excitatory junction potentials (s.e.j.p.s) recorded from guinea-pig vas deferens were greatly reduced or abolished by alpha, beta-methylene-ATP, the stable analogue of adenosine 5'-triphosphate (ATP). Brief (20-50 ms) local application of ATP by pressure ejection from a micropipette produced a transient depolarisation comparable to the e.j.p. Noradrenaline (NA) applied in a similar manner produced no such response. The depolarisation produced by the local application of ATP was also inhibited by alpha, beta-methylene-ATP. Superfusion of the tissue with ATP or NA produced depolarisation of muscle cells; in the presence of alpha, beta-methylene-ATP the depolarisation produced by ATP was almost abolished, whereas that produced by NA was not reduced. These results are consistent with the hypothesis that the e.j.p.s in the guinea-pig vas deferens are mediated by ATP, acting as a cotransmitter with NA in the sympathetic nerves supplying this organ.