Human cardiac inwardly-rectifying K+ channel Kir(2.1b) is inhibited by direct protein kinase C-dependent regulation in human isolated cardiomyocytes and in an expression system.
BACKGROUND
Protein kinases A (PKA) and C (PKC) are activated in ischemic preconditioning and heart failure, conditions in which patients develop arrhythmias. The native inward rectifier potassium current (IK1) plays a central role in the stabilization of the resting membrane potential and the process of arrhythmogenesis. This study investigates the functional relationship between PKC and IK1.


RESULTS
In whole-cell patch-clamp experiments with isolated human atrial cardiomyocytes, the IK1 was reduced by 41% when the nonspecific activator of PKC phorbol 12 myristate 13-acetate (PMA; 100 nmol/L) was applied. To investigate the effects of PKC on cloned channel underlying parts of the native IK1, we expressed Kir(2.1b) heterologously in Xenopus oocytes and measured currents with the double-electrode voltage-clamp technique. PMA decreased the current by an average of 68%, with an IC50 of 0.68 nmol/L. The inactive compound 4-alpha-PMA was ineffective. Thymeleatoxin and 1-oleolyl-2-acetyl-sn-glycerol, 2 specific activators of PKC, produced effects similar to those of PMA. Inhibitors of PKC, ie, staurosporine and chelerytrine, could inhibit the PMA effect (1 nmol/L) significantly. After mutation of the PKC phosphorylation sites (especially S64A and T353A), PMA became ineffective.


CONCLUSIONS
The human IK1 in atrial cardiomyocytes and one of its underlying ion channels, the Kir(2.1b) channel, is inhibited by PKC-dependent signal transduction pathways, possibly contributing to arrhythmogenesis in patients with structural heart disease in which PKC is activated.
Karle
Christoph A
CA
Department of Cardiology, University of Heidelberg Medical School, Heidelberg, Germany.
Zitron
Edgar
E
Zhang
Wei
W
Wendt-Nordahl
Gunnar
G
Kathöfer
Sven
S
Thomas
Dierk
D
Gut
Bernd
B
Scholz
Eberhard
E
Vahl
Christian-Friedrich
CF
Katus
Hugo A
HA
Kiehn
Johann
J
D000595:Amino Acid Sequence; D000818:Animals; D016275:Atrial Function; D002478:Cells, Cultured; D004553:Electric Conductivity; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006321:Heart / Q000502:physiology*; D006325:Heart Atria / Q000166:cytology / Q000187:drug effects; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009206:Myocardium / Q000201:enzymology*; D009865:Oocytes / Q000378:metabolism; D010766:Phosphorylation; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D016415:Sequence Alignment; D013755:Tetradecanoylphorbol Acetate / Q000037:antagonists & inhibitors / Q000494:pharmacology; D014981:Xenopus
D004791:Enzyme Inhibitors; D024661:Potassium Channels, Inwardly Rectifying; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate