Steady-state and closed-state inactivation properties of inactivating BK channels.
Calcium-dependent potassium (BK-type) Ca2+ and voltage-dependent K+ channels in chromaffin cells exhibit an inactivation that probably arises from coassembly of Slo1 alpha subunits with auxiliary beta subunits. One goal of this work was to determine whether the Ca2+ dependence of inactivation arises from any mechanism other than coupling of inactivation to the Ca2+ dependence of activation. Steady-state inactivation and the onset of inactivation were studied in inside-out patches and whole-cell recordings from rat adrenal chromaffin cells with parallel experiments on inactivating BK channels resulting from cloned alpha + beta2 subunits. In both cases, steady-state inactivation was shifted to more negative potentials by increases in submembrane [Ca2+] from 1 to 60 microM. At 10 and 60 microM Ca2+, the maximal channel availability at negative potentials was similar despite a shift in the voltage of half availability, suggesting there is no strictly Ca2+-dependent inactivation. In contrast, in the absence of Ca2+, depolarization to potentials positive to +20 mV induces channel inactivation. Thus, voltage-dependent, but not solely Ca2+-dependent, kinetic steps are required for inactivation to occur. Finally, under some conditions, BK channels are shown to inactivate as readily from closed states as from open states, indicative that a key conformational change required for inactivation precedes channel opening.
Ding
Jiu Ping
JP
Washington University School of Medicine, Department of Anesthesiology, St. Louis, Missouri 63110, USA.
Lingle
Christopher J
CJ
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000502:physiology*; D004594:Electrophysiology / Q000379:methods; D005260:Female; D015640:Ion Channel Gating / Q000502:physiology*; D007700:Kinetics; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000235:genetics / Q000502:physiology*; D018075:RNA, Complementary / Q000235:genetics; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014982:Xenopus laevis
C494842:Kcnma1 protein, rat; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D018075:RNA, Complementary; D011994:Recombinant Proteins; D002118:Calcium