Human cardiac inwardly rectifying current IKir2.2 is upregulated by activation of protein kinase A.
OBJECTIVE
The cardiac inwardly rectifying potassium current IK1 and its molecular correlates Kir2.1 and Kir2.2 play an important role in cardiac repolarisation and in the pathogenesis of hereditary long-QT syndrome (LQTS-7). Protein kinases A (PKA) and C (PKC) are key enzymes in adrenergic signal transduction, inducing arrhythmias in heart disease. This study investigated the regulation of Kir2.2 (KCNJ12) by PKA.


METHODS
Cloned Kir2.2 channels were expressed heterologously in Xenopus oocytes and currents were measured with the double-electrode voltage-clamp technique.


RESULTS
After activation of PKA by forskolin (100 micromol/l) or Ro-20-1724 (100 micromol/l), wild type currents at -120 mV were increased by 93.7% and 79.0%, respectively. Coapplication of the PKA inhibitor KT-5720 (2.5 micromol/l) attenuated this effect. No significant changes were apparent after mutation of the single PKA consensus site S430. In addition, removal of all four PKC consensus sites in Kir2.2 induced a phorbolester-mediated current increase which could be suppressed by PKA inhibitors H-89 (50 micromol/l) and KT-5720 (2.5 micromol/l).


CONCLUSIONS
This study demonstrates antagonistic effects of PKA and PKC in the regulation of Kir2.2. Phosphorylation by PKC has been shown to cause an inhibition of Kir2.2 currents, whereas activation of PKA leads to current upregulation.
Department of Cardiology, Medical University Hospital Heidelberg, Bergheimerstrasse 58, D-69115, Heidelberg, Germany.
Edgar
E
Zitron
Claudia
C
Kiesecker
Sonja
S
Lück
Sven
S
Kathöfer
Dierk
D
Thomas
Volker A W
VA
Kreye
Johann
J
Kiehn
Hugo A
HA
Katus
Wolfgang
W
Schoels
Christoph A
CA
Karle
D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008133:Long QT Syndrome / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D014981:Xenopus
D024661:Potassium Channels, Inwardly Rectifying; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C