A TEA-insensitive flickering potassium channel active around the resting potential in myelinated nerve.
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 (PNa/PK = 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 (tau o = 0.09 msec), closed times with the sum of three exponentials (tau 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 Em = -90 mV (IC50 = 1.1 mM). Ba and, more potently, Zn ions lowered not only the apparent single-channel 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.
Koh
D S
DS
Physiologisches Institut, Justus-Liebig-Universität, Giessen, Germany.
Jonas
P
P
Bräu
M E
ME
Vogel
W
W
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D001464:Barium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D002586:Cesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D013757:Tetraethylammonium Compounds / Q000494:pharmacology*; D014982:Xenopus laevis; D015032:Zinc / Q000494:pharmacology
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D002586:Cesium; D001464:Barium; D015032:Zinc