Increase of the single-channel conductance of KvLQT1 potassium channels induced by the association with minK

Abstract

Gating of the delayed rectifier K+ channel KvLQT1 is drastically slowed by the association with the small membrane protein minK and it is thought that the KvLQT1/minK complex underlies the slow delayed rectifier K+ current of cardiac cells. There is controversy about the effects of the association between KvLQT1 and minK on the single-channel conductance. Here, nonstationary fluctuation analysis was applied to inward K+ tail currents recorded with a high-time resolution (5 kHz bandwidth) from macropatches of homomeric KvLQT1 and heteromeric KvLQT1/minK channels expressed in Xenopus oocytes to estimate their single-channel conductance. It was found that heteromers have a threefold larger conductance (5.8 pS) compared to homomeric channels (1.8 pS) in symmetrical high-K+ solutions. The larger conductance of heteromers explains in part their larger macroscopic conductance in heterologous expression systems. The molecular mechanism underlying the conductance increase remains to be identified.

Novel Kv7.1-Phosphatidylinositol 4,5-Bisphosphate Interaction Sites Uncovered by Charge Neutralization Scanning

“…Four mutants showed reduced stimulation (marked in blue; K183C, R190C, R249C, and K354C) to values between 120 and 150%. In contrast, currents of mutants shown in red (R181C, R192C, R259C, R360C, and K362C) were either not affected or even significantly decreased by up to 25% upon diC 8 , showing all six transmembrane segments S1-S6 with pore loop and selectivity filter sequence GYG. Shown are all amino acids included in this study.…”

“…2A). To discover different properties upon diC 8 -PIP 2 application, we analyzed current amplitudes. The amplitudes at 40 mV were normalized to the respective current without the PIP 2 analog diC 8 -PIP 2 of each individual batch (Fig.…”

“…Although K v 7.1 can assemble with all five members of the KCNE ␤-subunit family, its interaction with KCNE1 (also called minK or IsK) is best described (1,(3)(4)(5)(6)(7). The noninactivating K v 7.1/KCNE1 channel complex shows slow activation and deactivation kinetics (1,4,8,9). These channels mediate the slowly activating cardiac potassium current I Ks (1,3), which contributes to the repolarization of myocyte membranes during phase 3 of the cardiac action potential (10,11).…”

“…These were coexpressed with KCNE1 in Xenopus laevis oocytes to form slowly activating (I Ks ) channels. Effects of injected diC 8 -PIP 2 on wild type and mutant channels was investigated by means of the two-electrode voltage-clamp. Included in the charge neutralization scan were the residues identified by Thomas et al (35).…”

Single-channel basis for the slow activation of the repolarizing cardiac potassium current, I Ks

“…Several groups have determined from noise variance analysis that KCNE1 either decreases (13) or increases the single-channel conductance of KCNQ1 three-to fivefold, but the reported conductance for I Ks varies among these studies, in part because the rapid flicker activity of the channel complicates accurate measurements of variance (12,14,15). Yang and Sigworth (12) suggested a singlechannel conductance, based on noise analysis at +50 mV, of 4.5 or 6.5 pS for human KCNQ1 expressed with human or rat KCNE1, respectively, in Xenopus.…”