Antagonism of the neuromuscular blocking effect of polymyxin B by 3,4-diaminopyridine

Polymyxin B (0.2 mg/ml) depressed the contractile response of rat diaphragm to indirect stimulation, decreased the amplitude of end-plate potential and blocked the neuromuscular transmission at last. 3,4-Diaminopyridine (0.l mmol/L) antagonized this inhibitory effect. It increased the amplitude of end-plate potential and restored the neuromuscular transmission. The twitch respones recovered immediately after the addition of 3,4-diaminopyridine (0.2 mmol/L) and exceeded its control. However, the antagonistic effect of 3,4- diaminopyridine lasted only 1.5-2 h. The miniature end-plate potential abolished by polymyxin B did not reappear after the administration of 3,4-diaminopyridine.