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Probing the mechanisms underlying modulation of quinidine sensitivity to cardiac I Ks block by protein kinase A‐mediated I Ks phosphorylation
Author(s) -
Yang Tao,
Kanki Hideaki,
Zhang Wei,
Roden Dan M
Publication year - 2009
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2009.00293.x
Subject(s) - quinidine , chemistry , protein kinase a , stimulation , prepulse inhibition , phosphorylation , biophysics , pharmacology , gating , medicine , endocrinology , biochemistry , biology , schizophrenia (object oriented programming) , psychiatry
Background and purpose: Cardiac I Ks is enhanced by protein kinase A (PKA) stimulation. And PKA‐stimulated I Ks is about threefold less sensitive to quinidine block than basal current. In this study, we further tested two competing hypotheses: I Ks phosphorylation either (i) modulates access of blocking drugs to a binding site; or (ii) destabilizes the drug–channel interaction. Experimental approach: To distinguish between these hypotheses, we studied quinidine block of I Ks channels in which three PKA site residues of the α‐subunit KCNQ1 were mutated with a bulky negative charged aspartic acid (D). To study alleviation of I Ks block by quinidine, we compared activating current at +60 mV, either with or without 5 s hyperpolarizing prepulses to −120 mV. Key results: Without PKA stimulation, quinidine (100 µM) blocked wild‐type current to a similar extent with and without the prepulse (93 ± 2% of pre‐drug current at +60 mV vs. 95 ± 1%). With PKA‐stimulated wild‐type channels, however, there was less block with the hyperpolarization to −120 mV: at +60 mV, block was 71 ± 2% (−prepulse) versus 58 ± 3% (+prepulse). Individual D‐mutations and the triple‐D mutant were resistant to quinidine block similar to that seen with PKA‐stimulated wild‐type I Ks . Conclusions and implications: We conclude that phosphorylation‐induced insertion of bulky negative charges alleviates quinidine block and that PKA‐induced stimulation, by conferring negative charges to the channels, blunts I Ks block as the interaction between the channels and blockers becomes destabilized. These effects would be of clinical significance in providing protective mechanisms against pro‐arrhythmias caused by drug‐induced inhibition of I Ks and I Kr .