CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING |
Endogenous KCNE subunits govern Kv2.1 K+ channel activation kinetics in Xenopus oocyte studies
Earl Gordon 1, Torsten K. Roepke 1 and Geoffrey W. Abbott 1*
1 Weill Medical College of Cornell University
* To whom correspondence should be addressed. E-mail: gwa2001{at}med.cornell.edu.
Submitted on August 11, 2005
Revised on September 15, 2005
Accepted on 7 November 2005
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Abstract |
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Kv2.1 is a voltage-gated potassium (Kv) channel that generates delayed rectifier currents in mammalian heart and brain. The biophysical properties of Kv2.1 and other ion channels have been characterized by functional expression in heterologous systems, and most commonly in Xenopus laevis oocytes. A number of previous oocyte-based studies of mammalian potassium channels have revealed expression level-dependent changes in channel properties, leading to the suggestion that endogenous oocyte factors regulate channel gating. Here, we show that endogenous oocyte potassium channel KCNE ancillary subunits xMinK and xMiRP2 slow the activation of oocyte-expressed mammalian Kv2.1 channels 2-4 fold. This produces a sigmoidal relationship between Kv2.1 current density and activation rate in oocyte-based two-electrode voltage clamp studies. The effect of endogenous xMiRP2 and xMinK on Kv2.1 activation is diluted at high Kv2.1 expression levels, or by RNAi knockdown of either endogenous subunit. RNAi knockdown of both xMiRP2 and xMinK eliminates the correlation between Kv2.1 expression level and activation kinetics. The data demonstrate a molecular basis for expression level-dependent changes in Kv channel gating observed in heterologous expression studies.
Key Words:
KCNE1, KCNE3, MiRP2, MinK, RNAi, delayed rectifier
