[Effect of yohimbine and tetrodotoxin on asymmetric displacement currents of nodes of Ranvier].

The indole alkaloid yohimbine (40 microM in the outside solution) is shown to reduce the intramembrane charge transferred by the asymmetric displacement current in the frog Ranvier node by 40%, the sodium permeability being inhibited by more than 90%. However, when tetrodotoxin (0.3 microM) was present in the outside solution, yohimbine inhibited the displacement charge only by a few per cent. The data indicate that the occlusion of the external mouth of Na channel by tetrodotoxin hinders the yohimbine (a lipid-soluble substance) effect on asymmetric displacement currents and supposed to affect Na channels from the membrane lipids and partly from the axoplasm. The possible interaction of Na channel blocking agents which are different both in chemical properties and in the modes of action on Na channels should be taken into consideration in the experiments with asymmetric displacement currents.