Human axons contain at least five types of voltage-dependent potassium channel

• Published in: The Journal of physiology Vol. 518; no. 3; pp. 681 - 696
• Main Authors: Reid, Gordon, Scholz, Andreas, Bostock, Hugh, Vogel, Werner
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01.08.1999; Blackwell Science Ltd; Blackwell Science Inc
• Subjects: Adolescent; Adult; Animals; Axons - drug effects; Axons - physiology; Elapid Venoms - pharmacology; Electric Stimulation; Electrophysiology; Humans; In Vitro Techniques; Ion Channel Gating - drug effects; Ion Channel Gating - physiology; Isoquinolines; Kinetics; Membrane Potentials - drug effects; Membrane Potentials - physiology; Middle Aged; Nerve Fibers, Myelinated - drug effects; Nerve Fibers, Myelinated - physiology; Original; Patch-Clamp Techniques; Potassium Channel Blockers; Potassium Channels - physiology; Rats
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.1999.0681p.x

We investigated voltage-gated potassium channels in human peripheral myelinated axons; apart from the I, S and F channels already described in amphibian and rat axons, we identified at least two other channel types. The I channel activated between -70 and -40 mV, and inactivated very slowly (time constant 13.1 s at -40 mV). It had two gating modes: the dominant (‘noisy’) mode had a conductance of 30 pS (inward current, symmetrical 155 mM K + ) and a deactivation time constant (τ) of 25 ms (-80 mV); it accounted for most (≈50-75 %) of the macroscopic K + current in large patches. The secondary (‘flickery’) gating mode had a conductance of 22 pS, and showed bi-exponential deactivation (τ = 16 and 102 ms; -80 mV); it contributed part of the slow macroscopic K + current. The I channel current was blocked by 1 μM α-dendrotoxin (DTX); we also observed two other DTX-sensitive K + channel types (40 pS and 25 pS). The S and F channels were not blocked by 1 μM DTX. The conductance of the S channel was 7-10 pS, and it activated at slightly more negative potentials than the I channel; its deactivation was slow (τ= 41.7 ms at -100 mV). It contributed a second component of the slow macroscopic K + current. The F channel had a conductance of 50 pS; it activated at potentials between -40 and +40 mV, deactivated very rapidly (τ = 1.4 ms at -100 mV), and inactivated rapidly (τ= 62 ms at +80 mV). It accounted for the fast-deactivating macroscopic K + current and partly for fast K + current inactivation. We conclude that human and rat axonal K + channels are closely similar, but that the correspondence between K + channel types and the macroscopic currents usually attributed to them is only partial. At least five channel types exist, and their characteristics overlap to a considerable extent.