| Abstract: | Variations in the structure of Ranvier nodes and of the paranodal region of frog nerve fibers were examined in an intravital light-optical investigation. Several morphological characteristics of the degree of disturbance of the structures of the paranodal zone (myelin cones and bulbs of the node) are compared. Morphological characteristics for the same isolated nerve fibers were compared with electrophysiological characteristics obtained by the voltage clamp method. A definite parallel was found between the degree of morphological changes in the paranodal myelin and the fall in the maximal sodium and potassium conductances of the membrane, while the leakage conductance remained relatively constant. The lower resistance of the sodium and potassium systems to injurious factors evidently reflects the more complex molecular organization of the excitable (sodium and potassium) than of the leakage channels. Considerable changes in the properties of the sodium channels caused by batrachotoxin were not accompanied by any visible changes in the paranodal regions of the myelin sheath. The results are examined from the standpoint of modern views regarding the nature of axo-glial relations in the nerve fiber.A. V. Vishnevskii Institute of Surgery, Academy of Medical Sciences of the USSR, Moscow. I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 10, No. 4, pp. 400–406, July–August, 1978. |
