Kv4 channels exhibit modulation of closed-state inactivation in inside-out patches.
The mechanisms of inactivation gating of the neuronal somatodendritic A-type K(+) current and the cardiac I(to) were investigated in Xenopus oocyte macropatches expressing Kv4.1 and Kv4.3 channels. Upon membrane patch excision (inside-out), Kv4.1 channels undergo time-dependent acceleration of macroscopic inactivation accompanied by a parallel partial current rundown. These changes are readily reversible by patch cramming, suggesting the influence of modulatory cytoplasmic factors. The consequences of these perturbations were investigated in detail to gain insights into the biophysical basis and mechanisms of inactivation gating. Accelerated inactivation at positive voltages (0 to +110 mV) is mainly the result of reducing the time constant of slow inactivation and the relative weight of the slow component of inactivation. Concomitantly, the time constants of closed-state inactivation at negative membrane potentials (-90 to -50 mV) are substantially decreased in inside-out patches. Deactivation is moderately accelerated, and recovery from inactivation and the peak G--V curve exhibit little or no change. In agreement with more favorable closed-state inactivation in inside-out patches, the steady-state inactivation curve exhibits a hyperpolarizing shift of approximately 10 mV. Closed-state inactivation was similarly enhanced in Kv4.3. An allosteric model that assumes significant closed-state inactivation at all relevant voltages can explain Kv4 inactivation gating and the modulatory changes.
Beck
E J
EJ
Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College at Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Covarrubias
M
M
D000494:Allosteric Regulation; D000818:Animals; D003712:Dendrites / Q000378:metabolism; D004553:Electric Conductivity; D015640:Ion Channel Gating; D007700:Kinetics; D008564:Membrane Potentials; D051379:Mice; D008954:Models, Biological; D009206:Myocardium / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D051672:Shal Potassium Channels; D014982:Xenopus laevis
C497016:Kcnd1 protein, mouse; C497017:Kcnd1 protein, rat; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051672:Shal Potassium Channels