Ultra-slow inactivation of the ionic currents through the membrane of myelinated nerve.
(1) Voltage-clamp experiments were performed with myelinated fibres isolated from the sciatic nerve of the frog to study slow changes of the specific sodium and potassium currents as a function of membrane (holding) potential and time. (2) The level of the peak sodium current depends on holding potential VH. This dependence can be described by a sigmoidal function uinfinity(VH). The underlying process is called "ultra-slow sodium inactivation" and is different and separable from the short time steady-state inactivation, hinfinity(V), and from the slow inactivation depending on the extracellular potassium concentration (Adelman, Jr., W. J. and Palti, Y. (1969), J Gen. Physiol. 54, 589-606; Peganov, E. M., Khodorov, B.I. and Shishkova, L. D. (1973), Bull. Exp. Biol. Med. 25, 15-19; Khodorov, B. I. Shishkova, L. D. and Peganov, E. M. (1974), Bull. Exp. Biol. Med. 3, 10-14). (3) After a sudden change of the holding potential the sodium current reaches a new steady-state level (due to the transition of uinfinity(VH) to the corresponding value) within approx. 4 min. The kinetics of the transition cannot be described by a single exponential function. (4) A corresponding voltage- and time-dependent process of ultra-slow inactivation exists for the potassium current in the node of Ranvier. The kinetics are faster than those of the sodium system.
D000818:Animals; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D003201:Computers; D008564:Membrane Potentials / Q000187:drug effects; D009186:Myelin Sheath / Q000187:drug effects / Q000502:physiology*; D011199:Potentiometry; D011893:Rana esculenta; D012584:Sciatic Nerve / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology
D012964:Sodium