Effects of reserpine pretreatment on neuroeffector transmission in the vas deferens

1. The effects of reserpine pretreatment on neurotransmission in the guinea-pig vas deferens have been re-examined with a view to study the role of noradrenaline (NA) in mediating postjunctional electrical responses and, in particular, excitatory junction potentials (EJP). 2. Reserpine (5 mg/kg, i.p.) caused almost total depletion (below detection levels) of the NA content of the vas deferens. However, spontaneous and evoked excitatory junction potentials (SEJP, EJP) and currents (SEJC, EJC) could still be recorded in NA-depleted tissues. The amplitude distribution of SEJC in control and reserpinized tissues was similar. 3. Facilitation of EJP and EJC was markedly slowed in reserpinized tissues, EJP taking 50-60 pulses to facilitate fully. However the amplitudes of fully facilitated EJP were comparable to EJP recorded in control tissues. 4. EJPs in reserpinized vasa deferentia were unaffected by the NA synthesis inhibitor, alpha-methyl tyrosine, but were abolished in the presence of the stable ATP analogue alpha,beta-methylene ATP which desensitizes postjunctional P2-purinoceptors. 5. Local application of ATP, but not NA, mimicked the EJP. These results indicate that EJP are mediated by a non-noradrenergic neurotransmitter possibly ATP.