© 2003 by European Society of Cardiology
Copyright © 2003, European Society of Cardiology
Regulation of HERG potassium channel activation by protein kinase C independent of direct phosphorylation of the channel protein
aDepartment of Cardiology, Medical University Hospital Heidelberg, Bergheimerstrasse 58, D-69115 Heidelberg, Germany
bDepartment of Physiology and Pathophysiology, University of Heidelberg, Im Neuenheimer Feld 326, D-69120 Heidelberg, Germany
dthomas{at}ix.urz.uni-heidelberg.de
* Corresponding author. Tel.: +49-6221-568611; fax: +49-6221-565515.
Objective: Patients with HERG-associated long QT syndrome typically develop tachyarrhythmias during physical or emotional stress. Previous studies have revealed that activation of the beta-adrenergic system and consecutive elevation of the intracellular cAMP concentration regulate HERG channels via protein kinase A-mediated phosphorylation of the channel protein and via direct interaction with the cAMP binding site of HERG. In contrast, the influence of the alpha-adrenergic signal transduction cascade on HERG currents as suggested by recent reports is less well understood. The aim of the present study was to elucidate the biochemical pathways of the protein kinase C (PKC)-dependent regulation of HERG currents. Methods: HERG channels were heterologously expressed in Xenopus laevis oocytes, and currents were measured using the two-microelectrode voltage clamp technique. Results: Application of the phorbol ester PMA, an unspecific protein kinase activator, shifted the voltage dependence of HERG activation towards more positive potentials. This effect could be mimicked by activation of conventional PKC isoforms with thymeleatoxin. Coexpression of HERG with the beta-subunits minK or hMiRP1 did not alter the effect of PMA. Specific inhibition of PKC abolished the PMA-induced activation shift, suggesting that PKC is required within the regulatory mechanism. The PMA-induced effect could still be observed when the PKC-dependent phosphorylation sites in HERG were deleted by mutagenesis. Cytoskeletal proteins such as actin filaments or microtubules did not affect the HERG activation shift. Conclusion: In addition to the known effects of PKA and cAMP, HERG channels are also modulated by PKC. The molecular mechanisms of this PKC-dependent process are not completely understood but do not depend on direct PKC-dependent phosphorylation of the channel.
KEYWORDS HERG, human ether-a-go-go-related gene; hMiRP1, human mink-related peptide 1; PKA, protein kinase A; PKC, protein kinase C; aPKC, atypical PKC isoforms; cPKC, conventional PKC isoforms; nPKC, novel PKC isoforms; PMA, phorbol 12-myristate-13-acetate; ICa, L-type calcium current; IK, delayed rectifier potassium current; IKr, rapidly activating component of IK; IKs, slowly activating component of IK; IK1, inward rectifier potassium current; IK,ATP, ATP-sensitive potassium current; IKur, ultra-rapid potassium current; INa, sodium current; Ito, transient outward potassium current; LQTS, long QT syndrome; minK, minimal K+ channel; V1/2, half-maximal activation voltage; 
V1/2, shift of the half-maximal activation voltage
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