A TEA-insensitive flickering potassium channel active around the resting potential in myelinated nerve

Summary

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.