Changes in the electrical activity of a single node of Ranvier of an isolated nerve fiber due to novocain

Abstract

A solution of novocain in small concentrations (1·10−8 and 1·10−7) does not cause changes of action potential (AP) amplitude and threshold of depolarization (ΔV) in the node of Ranvier of isolated frog's nerve fiber. A novocain concentration of 5·10−5 causes a reduction of response amplitude and a rise of the depolarization threshold. Responses are graded, i.e., increase with an increase in the strength of its stimulus. Novocain solution in a concentration of 1·10−4 depresses AP in the node and causes a rise of threshold of depolarization up to 200%. Changes caused by novocain are usually not completely reversible even after long wash-off. Electrical activity, depressed by novocain in the node of Ranvier restored by the action of a direct current anode. If anode voltage is sufficiently large, the AP is completely restored and the threshold of depolarization is at the same level as before. The effect of a direct current cathode is similar to that of novocain. A cathode current causes a sharp fall of AP and a considerable rise of the threshold of depolarization. The possible mechanism of the novocain action and the restorative effect of the direct current anode is discussed.