A novel potassium-selective channel which is active at membrane potentials between — 100 mV and +40 mV has been identified in peripheral myelinated axons of Xenopus laevis using the patch-clamp technique. At negative potentials with 105 mm-K on both sides of the membrane, the channel at 1 kHz resolution showed a series of brief openings and closings interrupted by longer closings, resulting in a flickery bursting activity. Measurements with resolution up to 10 kHz revealed a single-channel conductance of 49 pS with 105 mm-K and 17 pS with 2.5 mm-K on the outer side of the membrane. The channel was selective for K ions over Na ions (P Na/P K = 0.033). The probability of being within a burst in outside-out patches varied from patch to patch (>0.2, but often >0.9), and was independent of membrane potential. Open-time histograms were satisfactorily described with a single exponential (τ o= 0.09 msec), closed times with the sum of three exponentials (τ c= 0.13, 5.9, and 36.6 msec). Sensitivity to external tetraethylammonium was comparatively low (IC50 = 19.0 mm). External Cs ions reduced the apparent unitary conductance for inward currents at E m= −90 mV (IC50 = 1.1 mm). Ba and, more potently, Zn ions lowered not only the apparent singlechannel conductance but also open probability. The local anesthetic bupivacaine with high potency reduced probability of being within a burst (IC50 = 165 nm). The flickering K channel is clearly different from the other five types of K channels identified so far in the same preparation. We suggest that this channel may form the molecular basis of the resting potential in vertebrate myelinated axons.
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A grant from the Konrad-Adenauer-Stiftung to D.-S.K. is gratefully acknowledged, and this paper constitutes a part of his dissertation. We thank Drs. H. Bostock, B. Neumcke, D. Siemen and Mr. G. Reid for reading the manuscript and Mrs. Elke Schmidt for technical assistance. Financial support was received from the Deutsche Forschungsgemeinschaft (Vol88/13-2).
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Koh, DS., Jonas, P., Bräu, M.E. et al. A TEA-insensitive flickering potassium channel active around the resting potential in myelinated nerve. J. Membarin Biol. 130, 149–162 (1992). https://doi.org/10.1007/BF00231893
- patch clamp
- myelinated nerve fiber
- potassium channel
- flicker kinetics
- resting potential