The cole-moore effect in nodal membrane of the frogRana ridibunda: Evidence for fast and slow potassium channels |
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Authors: | V. I. Ilyin Irene E. Katina A. V. Lonskii V. S. Makovsky E. V. Polishchuk |
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Affiliation: | (1) Institute of Physiology, Leningrad University, 199164 Leningrad, USSR;(2) Leningrad Nuclear Physics Institute, Academy of Science USSR, 188350 Gatchina, Leningrad District, USSR;(3) Institute of Cytology, Academy Science USSR, 190121 Leningrad, USSR |
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Abstract: | Summary The K conductance (gK) kinetics were studied in voltage-clamped frog nodes (Rana ridibunda) in double-pulse experiments. The Cole-Moore translation forgK–t curves associated with different initial potentials (E) was only observed with a small percentage of fibers. The absence of the translation was found to be caused by the involvement of an additional, slow,gK component. This component cannot be attributed to a multiple-state performance of the K channel. It can only be accounted for by a separate, slow K channel, the fast channel being the same as then4 K channel inR. pipiens.The slow K channel is characterized by weaker sensitivity to TEA, smaller density, weaker potential (E) dependence, and somewhat more negativeE range of activation than the fast K channel. According to characteristics of the slow K system, three types of fibers were found. In Type I fibers (most numerous) the slow K channel behaves as ann4 HH channel. In Type II fibers (the second largest group found) the slow K channel obeys the HH kinetics within a certainE range only; beyond this range the exponential decline of the slowgK component is preceded by anE-dependent delay, its kinetics after the delay being the same as those in Type I fibers. In Type III fibers (rare) the slow K channel is lacking, and it is only in these fibers that the Cole-Moore translation of the measuredgK–t curves can be observed directly.The physiological role of the fast and slow K channel in amphibian nerves is briefly discussed. |
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Keywords: | Ranvier node potassium currents Hodgkin-Huxley kinetics potassium channel conductance states |
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