The effect of primycin, an antibiotic known to inhibit potassium conductance, was studied on acetylcholine (ACh) release from the nerve terminals of the Auerbach plexus and cortical slice of the rat. Primycin enhanced the resting release of ACh; however, it failed to affect the amount of ACh released by a single shock. It has no effect on Na+K+-activated ATPase. Its effect on ACh release was prevented by tetrodotoxin and by Ca removal. It is concluded that its effect on potassium conductance might account for its ACh-releasing effect: it produces depolarization and spontaneous firing.
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