Human axons contain at least five types of voltage-dependent potassium channel
Article first published online: 7 SEP 2004
The Journal of Physiology
Volume 518, Issue 3, pages 681–696, August 1999
How to Cite
Reid, G., Scholz, A., Bostock, H. and Vogel, W. (1999), Human axons contain at least five types of voltage-dependent potassium channel. The Journal of Physiology, 518: 681–696. doi: 10.1111/j.1469-7793.1999.0681p.x
- Issue published online: 7 SEP 2004
- Article first published online: 7 SEP 2004
- (Received 22 February 1999; accepted after revision 6 May 1999)
- 1We 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.
- 2The 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.
- 3The 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.
- 4The 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.
- 5The 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.
- 6We 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.