| Abstract: | Experiments were carried out on single nerve fibers with a  covered node. The nerve fiber was isolated together with one to three fragments of neighboring fibers adjacent to the node and which were firmly connected to the nodal ends of the myelin sheath by means of numerous connective-tissue membranes, thereby strengthening the node and protecting it against stretching during dissection. In potassium-free solution after-hyperpolarization of the nerve fiber membrane with an amplitude of 2.7 mV develops immediately after the end of the spike. Its origin is connected with maintenance of the increased potassium permeability of the membrane. During repetitive stimulation of the covered node the amplitude of after-hyperpolarization falls successively, as a result of a decrease in the outward potassium current caused by a reduction in the potassium electrochemical gradient. These observations are regarded as confirmation of the hypothesis expressed previously on the existence of a diffusion barrier in the region of the Ranvier node due to accumulation of K+ in the juxtamembranous space.Department of Anatomy and Physiology of Man and Animals, Ul'yanovsk Pedagogic Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR V. N. Chernigovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 86, No. 11, pp. 517–519, November, 1978. |
