Phosphorylation of the IKs channel complex inhibits drug block: novel mechanism underlying variable antiarrhythmic drug actions.
BACKGROUND
IKs, an important repolarizing current in heart, is an antiarrhythmic drug target and is markedly increased by activation of protein kinase A (PKA; eg, by beta-adrenergic stimulation). Because beta-adrenergic stimulation is a frequent trigger of arrhythmias, we hypothesized that PKA stimulation inhibits drug block.


RESULTS
CHO cells were transfected with KCNQ1 cDNA (encoding the pore-forming subunit) with or without the ancillary subunit KCNE1. IC50 for quinidine block of basal IKs was 5.8+/-1.2 micromol/L, versus 19.9+/-3.2 micromol/L (P<0.01) for PKA-stimulated current. A similar >3-fold shift was apparent in the absence of KCNE1 and with the IKs-specific blocker chromanol 293B. The first current recorded after channels were held at rest and exposed to the drug was reduced approximately 40%, and further depolarizations increased the block with a time constant (tau) of 181+/-27 seconds. By contrast, PKA-stimulated channels displayed a <5% first-pulse block and much slower block development (tau=405+/-85 seconds). Alanine substitution at 3 potential PKA target sites (S27, S468, and T470) generated an IKs that did not increase with PKA stimulation; this mutant retained wild-type drug sensitivity that was unaffected by PKA.


CONCLUSIONS
Activation of this key intracellular signaling pathway blunts drug block. The onset of block and the data with the PKA-resistant mutant support the concept that phosphorylation of the KCNQ1 subunit directly modulates drug access to a binding site on the channel. These data identify a novel mechanism for modulation of drug-channel interactions that may be especially important during beta-adrenergic stimulation.
Yang
Tao
T
Division of Clinical Pharmacology, Vanderbilt University School of Medicine, RRB532C, Nashville, TN 37232, USA.
Kanki
Hideaki
H
Roden
Dan M
DM
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D019943:Amino Acid Substitution; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D001145:Arrhythmias, Cardiac / Q000188:drug therapy*; D016466:CHO Cells; D006224:Cricetinae; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D046911:Macromolecular Substances; D010053:Ovary / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D011802:Quinidine / Q000494:pharmacology; D013329:Structure-Activity Relationship; D014162:Transfection
D000317:Adrenergic alpha-Antagonists; D000889:Anti-Arrhythmia Agents; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D046911:Macromolecular Substances; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D017868:Cyclic AMP-Dependent Protein Kinases; D011802:Quinidine