Interaction of polymyxin with vertebrate peripheral nerve axons

Abstract

The effect of the peptide antibiotic polymyxin on nerve membrane was investigated on the voltage clamped node of Ranvier. Low polymyxin concentrations (<2×10 −5 M) had little effect. Polymyxin (2×10 −5 −10 −4 M) produced a large increase in leakage conductance accompanied by large inward current and loss of evoked sodium currents. In choline-substituted Ringer's solution the increase in leakage conductance was small and potassium currents remained near control levels. Tetrodotoxin (10 −7 M) and calcium increased the threshold for the effect. Above 10 −4 M polymyxin, leakage conductance increased to levels associated with loss of membrane integrity. The results-suggest that polymyxin forms or opens Na and K-permeable channels in nerve membrane.