Functional modulation of the transient outward current Ito by KCNE beta-subunits and regional distribution in human non-failing and failing hearts.
OBJECTIVE
The function of Kv4.3 (KCND3) channels, which underlie the transient outward current I(to) in human heart, can be modulated by several accessory subunits such as KChIP2 and KCNE1-KCNE5. Here we aimed to determine the regional expression of Kv4.3, KChIP2, and KCNE mRNAs in non-failing and failing human hearts and to investigate the functional consequences of subunit coexpression in heterologous expression systems.


METHODS
We quantified mRNA levels for two Kv4.3 isoforms, Kv4.3-S and Kv4.3-L, and for KChIP2 as well as KCNE1-KCNE5 with real-time RT-PCR. We also studied the effects of KCNEs on Kv4.3+KChIP2 current characteristics in CHO cells with the whole-cell voltage-clamp method.


RESULTS
In non-failing hearts, low expression was found for KCNE1, KCNE3, and KCNE5, three times higher expression for KCNE2, and 60 times higher for KCNE4. Transmural gradients were detected only for KChIP2 in left and right ventricles. Compared to non-failing tissue, failing hearts showed higher expression of Kv4.3-L and KCNE1 and lower of Kv4.3-S, KChIP2, KCNE4, and KCNE5. In CHO cells, Kv4.3+KChIP2 currents were differentially modified by co-expressed KCNEs: time constants of inactivation were shorter with KCNE1 and KCNE3-5 while time-to-peak was decreased, and V(0.5) of steady-state inactivation was shifted to more negative potentials by all KCNE subunits. Importantly, KCNE2 induced a unique and prominent 'overshoot' of peak current during recovery from inactivation similar to that described for human I(to) while other KCNE subunits induced little (KCNE4,5) or no overshoot.


CONCLUSIONS
All KCNEs are expressed in the human heart at the transcript level. Compared to I(to) in native human myocytes, none of the combination of KChIP2 and KCNE produced an ideal congruency in current characteristics, suggesting that additional factors contribute to the regulation of the native I(to) channel.
Radicke
Susanne
S
Medical Faculty, Dresden University of Technology, Fetscherstr. 74, Dresden, 01307 Germany.
Cotella
Diego
D
Graf
Eva Maria
EM
Banse
Ulrich
U
Jost
Norbert
N
Varró
András
A
Tseng
Gea-Ny
GN
Ravens
Ursula
U
Wettwer
Erich
E
D000818:Animals; D016466:CHO Cells; D016022:Case-Control Studies; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D005786:Gene Expression Regulation; D006333:Heart Failure / Q000378:metabolism*; D006801:Humans; D051605:Kv Channel-Interacting Proteins / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051672:Shal Potassium Channels / Q000235:genetics / Q000378:metabolism*
C497021:KCND3 protein, human; C489622:KCNE1 protein, human; C489619:KCNE2 protein, human; C418492:KCNE3 protein, human; C498897:KCNE4 protein, human; C502068:KCNE5 protein, human; D051605:Kv Channel-Interacting Proteins; D024642:Potassium Channels, Voltage-Gated; D012333:RNA, Messenger; D051672:Shal Potassium Channels