DIFFERENCES IN THE RESPONSES TO PURINERGIC NERVE-STIMULATION AND APPLIED ATP IN THE GUINEA-PIG VAS-DEFERENS

The responses to sympathetic nerve stimulation and to applied ATP in t he guinea-pig vas deferens were compared. Nifedipine (10 mu M) markedl y reduced the non-adrenergic neural contraction but only partially blo cked the contractions produced by bath-applied ATP. Suramin (300 mu M) also markedly reduced the contractile responses produced by nerve sti mulation, but had no significant effect on the contractions produced b y bath-applied ATP. Using intracellular recording techniques, nerve st imulation was shown to produce an excitatory junction potential which was abolished by suramin (1 mu M). Ionophoretic application of ATP and bath-applied ATP also produced a depolarization. Suramin (1 mu M) fai led to abolish the response to bath-applied ATP and enhanced the ionop horetically induced depolarization. These results suggest either that ATP is not a transmitter in the vas deferens or that two classes of pu rinoceptor are present, one suramin-sensitive receptor which produces a contraction via the opening of voltage-dependent Ca2+ channels, and another which is suramin-resistant and produces a contraction by anoth er means.