GUANETHIDINE EFFECTS ON THE GUINEA-PIG VAS-DEFERENS ARE ANTAGONIZED BY THE BLOCKERS OF CALCIUM-ACTIVATED POTASSIUM CONDUCTANCE, APAMIN, METHYLENE-BLUE, AND QUININE

  • 1 January 1983
    • journal article
    • research article
    • Vol. 23  (2) , 409-416
Abstract
The blocking effects of guanethidine on electrically induced, neurally mediated, contractions of the guinea pig vas deferens in vitro could be markedly antagonized by the bee venom polypeptide apamin (20-60 nM), by 0.1 mM methylene blue and (less regularly) by 0.1-0.15 mM quinine, 3 substances known to inhibit Ca-activated K conductance in a variety of cells. Guanethidine (20 .mu.M) was inhibited (by 88%) the release of [3H]norepinephrine induced by electrical stimulation (20-Hz, 2-ms, biphasic pulses of supramaximal voltage). Such inhibition was decreased to 39% when 20 nM apamin was present together with guanethidine, thus showing that the effect of this polypeptide is presynaptic. Guanethidine may block adrenergic neurons by activating their Ca-activated K conductance, presumably by releasing intracellular Ca.