An activation gating switch in Kv1.2 is localized to a threonine residue in the S2-S3 linker.
ABSTRACT The activation properties of Kv1.2 channels are highly variable, with reported half-activation (V((1/2))) values ranging from approximately -40 mV to approximately +30 mV. Here we show that this arises because Kv1.2 channels occupy two distinct gating modes ("fast" and "slow"). "Slow" gating (tau(act) = 90 +/- 6 ms at +35 mV) was associated with a V((1/2)) of activation of +16.6 +/- 1.1 mV, whereas "fast" gating (tau(act) = 4.5 +/- 1.7 ms at +35 mV) was associated with a V((1/2)) of activation of -18.8 +/- 2.3 mV. It was possible to switch between gating modes by applying a prepulse, which suggested that channels activate to a single open state along separate "fast" and "slow" activation pathways. Using chimeras and point mutants between Kv1.2 and Kv1.5 channels, we determined that introduction of a positive charge at or around threonine 252 in the S2-S3 linker of Kv1.2 abolished "slow" activation gating. Furthermore, dialysis of the cytoplasm or excision of cell-attached patches from cells expressing Kv1.2 channels switched gating from "slow" to "fast", suggesting involvement of cytoplasmic regulators. Collectively, these results demonstrate two modes of activation gating in Kv1.2 and specific residues in the S2-S3 linker that act as a switch between these modes.
Article: Alteration of voltage-dependence of Shaker potassium channel by mutations in the S4 sequence.[show abstract] [hide abstract]
ABSTRACT: Voltage-dependent potassium, sodium and calcium ion channels may share a common mechanism of activation, in which the conserved S4 sequence acts as the primary voltage sensor. Site-directed mutagenesis of the S4 sequence of the Shaker potassium channel and electrophysiological analysis suggest that voltage-dependent activation involves the S4 sequence but is not solely due to electrostatic interactions.Nature 02/1991; 349(6307):305-10. · 36.28 Impact Factor
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ABSTRACT: Neurons owe their exquisite electrical excitability to voltage-gated ion channels. By creating and shaping the action potential, these voltage-sensitive proteins supply the neuron with crucial communication skills. A steady stream of experimental results, arising from numerous laboratories and employing a diverse repertoire of techniques, has produced a consensus model of the way voltage-gated ion channels sense and respond to changes in membrane potential. In contrast to this consensus mechanism, recent studies of the voltage-gated K(+) channel KvAP suggest a strikingly different mode of action. In this review, these disparate models are compared and critically discussed.Trends in Neurosciences 07/2004; 27(6):303-7. · 14.23 Impact Factor
Article: Identity of a novel delayed rectifier current from human heart with a cloned K+ channel current.[show abstract] [hide abstract]
ABSTRACT: In human myocardium, the nature of the K+ currents mediating repolarization of the action potential is still speculative. Delayed rectifier channels have recently been cloned from human myocardium, but it is unclear whether or not these currents are involved in the termination of the cardiac action potential plateau. In intact human atrial myocytes, we have identified a rapid delayed rectifier K+ current with properties and kinetics identical to those expressed by a K+ channel clone (fHK) isolated from human heart and stably incorporated into a human cell line for the first time. The myocyte current amplitude was 3.6 +/- 0.2 pA/pF (at +20 mV, n = 15) and activated with a time constant of 13.1 +/- 2 milliseconds at 0 mV (n = 15). The half-activation potential (V0.5) was -6 +/- 2.5 mV (n = 10) with a slope factor (k) of 8.6 +/- 2.2 (n = 10). The heterologously expressed fHK current amplitude was 136 pA/pF (at +20 mV, n = 9) with an activation time constant of 11.8 +/- 4.6 milliseconds at 0 mV; V0.5 was 4.1 +/- 2.4 mV (mean +/- SEM, n = 8); and k was 7.0. The conductance of single fHK channels was 16.9 picosiemens in 5 mM bath K+. Both native and cloned channel currents inactivated partially during sustained depolarizing pulses. Both currents were blocked by micromolar concentrations of 4-aminopyridine and were relatively insensitive to tetraethylammonium ions and class III antiarrhythmic agents.(ABSTRACT TRUNCATED AT 250 WORDS)Circulation Research 08/1993; 73(1):210-6. · 9.49 Impact Factor