Transmitter release and uptake evoked by the amphibian skin alkaloid, pumiliotoxin-B (PTX-B), in the electrically stimulated mouse vas deferens preparation (MVD)

1 Upon electrical stimulation three transmitters are known to be released f rom the adrenergic nerve terminals of the isolated MVD preparation: two mot or transmitters (noradrenaline (NA) and ATP) acting synergistically to prov oke twitch contraction, and an inhibitory transmitter, the peptide NPY. 2 The frog alkaloid pumiliotoxin-B (PTX-B) displayed two opposite effects o n the electrically stimulated MVD: at low concentrations (0.1-0.3 mu M) it caused twitch depression, at higher concentrations (0.5-2 mu M) there was a potent twitch stimulation. Transmitters and/or receptors involved in the d epressive effect could not be clearly identified, although interference wit h NPY is possible. On the other hand, the potent twitch stimulation caused by PTX-B may be due to exaggerated release of the same transmitters (NA and ATP) involved in twitch stimulation produced by electrical stimulation. 3 Opening by PTX-B of the Na+ channels on the membrane of the adrenergic ne rve terminals causes activation of the amine pump facilitating re-uptake of not only endogenous NA but also of exogenous catecholamines.