KCNE1 slows the voltage sensors of KCNQ1
Carlos A. Villalba-Galea: 0000-0002-6489-4651
Conference Title/Conference Publication
Biophysical Society 56th Annual Meeting
San Diego, CA
February 25-29, 2012
Date of Presentation
3, Supplement 1
KCNQ1 α-subunits assemble with KCNE1 forming the slow cardiac potassium channel IKs. KCNE1 alters currents of α-subunits by slowing activation and deactivation kinetics, suppressing inactivation, and increasing single-channel conductance. Attempts to elucidate the mechanism of KCNE1-induced slowing of kinetics have come to discrepant conclusions. Two studies using chemical modifiers and cys-substitution in the KCNQ1 S4 supported one model where KCNE1 acts on voltage-sensors alone and another where only the activation-gate is affected. A fluorimetric study argued for effects on sensors and the gate (Osteen et al, PNAS 2010). To address the controversy, we used cut-open oocyte vaseline-gap clamp to record gating currents, ionic currents and perform site-directed, voltage-clamp fluorimetry (VCF).
Gating currents show that voltage-sensor movement precedes pore opening in channels with only KCNQ1 α-subunits. VCF confirms this result. While ionic currents have a lag before activation, gating and fluorescence changes do not; this indicates a final concerted step after voltage sensors move before pore opening. In contrast, channels with KCNE1 show voltage-sensor movements with no lag that are ∼20-fold slower and mirror slowing of ionic current activation. These findings are unlike those made by Osteen et al. We used a smaller dye inserted closer to S4 and measured ionic current and fluorescence simultaneously in the same cells. We observe a matching and expected shift in the IKs fluorescence-voltage and ionic current-voltage relationships of +50 mV with KCNE1 and do not see voltage-sensor movements at hyperpolarized voltages as they report.
Both KCNQ1 and IKs channels have voltage-sensor kinetics almost as slow as ionic activation. Our simultaneous kinetic recordings of fluorescence and ionic currents support a model in which IKs channels are slowed purely by an effect of KCNE1 on the KCNQ1 voltage sensors. Support: HL105949 and GM030376.
Ruscic, Katarina; Miceli, Francesco; Villalba-Galea, Carlos A.; Bezanilla, Francisco; and Goldstein, Steve A. N., "KCNE1 slows the voltage sensors of KCNQ1" (2012). School of Pharmacy Faculty Presentations. 418.