Inactivation gating and 4-AP sensitivity in human brain Kv1.4 potassium channel.
Voltage-gated K(+) channels vary in sensitivity to block by 4-aminopyridine (4-AP) over a 1000-fold range. Most K(+) channel phenotypes with leucine at the fourth position (L4) in the leucine heptad repeat region, spanning the S4-S5 linker, exhibit low 4-AP sensitivity, while channels with phenylalanine exhibit high sensitivity. Mutational analysis on delayed rectifier type K(+) channels demonstrate increased 4-AP sensitivity upon mutation of the L4 heptad leucine to phenylalanine. This mutation can also influence inactivation gating, which is known to compete with 4-AP in rapidly inactivating A-type K(+) channels. Here, in a rapidly inactivating human brain Kv1.4 channel, we demonstrate a 400-fold increase in 4-AP sensitivity following substitution of L4 with phenylalanine. Accompanying this mutation is a slowing of inactivation, an acceleration of deactivation, and depolarizing shifts in the voltage dependence of activation and steady-state inactivation. To test the relative role of fast inactivation in modulating 4-AP block, N-terminal deletions of the fast inactivation gate were carried out in both channels. These deletions produced no change in 4-AP sensitivity in the mutant channel and approximately a six-fold increase in the wild type channel. These results support the view that changes at L4 which increase 4-AP sensitivity are largely due to 4-AP binding and may, in part, arise from alterations in channel conformation. Primarily, this study demonstrates that the fast inactivation gate is not a critical determinant of 4-AP sensitivity in Kv1.4 channels.
Department of Neurology, University of Maryland School of Medicine, BRB 12-040, 655 West Baltimore Street, Baltimore, MD 21201, USA. sjudge@umaryland.edu
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Judge
M J
MJ
Monteiro
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JZ
Yeh
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CT
Bever
D015761:4-Aminopyridine / Q000494:pharmacology*; D019943:Amino Acid Substitution; D001921:Brain / Q000187:drug effects*; D006801:Humans; D015640:Ion Channel Gating; D051665:Kv1.4 Potassium Channel; D007930:Leucine; D008564:Membrane Potentials / Q000187:drug effects; D009154:Mutation; D018408:Patch-Clamp Techniques; D010649:Phenylalanine; D015221:Potassium Channels / Q000187:drug effects*; D024642:Potassium Channels, Voltage-Gated
C496977:KCNA4 protein, human; D051665:Kv1.4 Potassium Channel; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D010649:Phenylalanine; D015761:4-Aminopyridine; D007930:Leucine