Abstract.
Single-channel properties of a delayed rectifier voltage-gated K+ channel (I-type) were investigated in peripheral myelinated axons from Xenopus laevis. Channels activated between −60 and −40 mV with a potential of half-maximal activation, E50, at −47.5 mV. Averaged single-channel currents activated with a time delay at all membrane potentials tested. Time to half-maximal activation decreased from 80 to 1.6 msec between −60 and +40 mV. The channel inactivated monoexponentially with a time constant of 10.9 sec at −40 mV. The time constant of deactivation was 126 msec at −80 mV and 16.9 msec at −110 mV. In symmetrical 105 mm K+, the single-channel conductance (γ) was 22 and 13 pS at negative and positive membrane potentials, respectively, at 13–15°C. In Na+-rich solution with 2.5 mm extracellular K+γ was 7 pS and the reversal potential was negative to −80 mV, indicating a high selectivity for K+ over Na+. γ depended on extracellular K+ concentration (K D = 19.6 mm) and temperature (Q 10= 1.45). External tetraethylammonium (TEA) reduced the apparent single-channel current amplitude at all potentials tested with a half-maximal inhibiting concentration (IC50) of 0.6 mm. Open probability of the channel, but not single-channel current amplitude was decreased by extracellular dendrotoxin (DTX, IC50= 6.8 nm) and mast cell degranulating peptide (MCDP, IC50= 41.9 nm). In Ringer solution the membrane potential of macroscopic I-channel patches was about −65 mV and depolarized under TEA and DTX. It is concluded that besides their activation during action potentials, I-channels may also stabilize the resting membrane potential.
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Received: 2 June 1995/Revised: 13 October 1995
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Koh, DS., Vogel, W. Single-Channel Analysis of a Delayed Rectifier K+ Channel in Xenopus Myelinated Nerve. J. Membrane Biol. 149, 221–232 (1996). https://doi.org/10.1007/s002329900022
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DOI: https://doi.org/10.1007/s002329900022