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Protein kinase C enhances the rapidly activating delayed rectifier potassium current, I Kr , through a reduction in C‐type inactivation in guinea‐pig ventricular myocytes
Author(s) -
Heath B. M.,
Terrar D. A.
Publication year - 2000
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2000.t01-2-00391.x
Subject(s) - isoprenaline , forskolin , chemistry , patch clamp , protein kinase c , staurosporine , inward rectifier potassium ion channel , potassium channel , protein kinase a , medicine , phorbol , endocrinology , pharmacology , biophysics , biochemistry , ion channel , kinase , biology , receptor , stimulation
The rapidly activating delayed rectifier potassium current, I Kr , was studied in guinea‐pig ventricular myocytes in the presence of thiopentone, which blocks the more slowly activating component of the delayed rectifier potassium current, I Ks , and using whole cell perforated patch clamp or switched voltage clamp with sharp electrodes to minimise intracellular dialysis. Activation of protein kinase A (PKA) by isoprenaline or forskolin caused an increase in I Kr tail currents. Following a 300 ms depolarising step to +20 mV, mean tail current amplitude was increased 47 ± 12% by isoprenaline, and 73 ± 13% by forskolin. No increase in I Kr was observed when I Kr was studied using whole cell ruptured patch clamp and there was no change in the reversal potential of I Kr in the presence of isoprenaline. The rectification of the current sensitive to E4031, a selective I Kr blocker, was markedly reduced in the presence of isoprenaline and the region of negative slope was absent. This is consistent with a reduction in the inactivation of I Kr and was supported by the finding that I Kr , in the presence of isoprenaline, was somewhat less sensitive to block. E4031 (5 μ m ) blocked only 81 ± 5% of I Kr in the presence of isoprenaline compared to 100 ± 0% in control. The forskolin‐ and isoprenaline‐induced increases in I Kr were inhibited by staurosporine and by the selective protein kinase C (PKC) inhibitor bisindolylmaleimide I. Direct activation of PKC by phorbol dibutyrate increased I Kr tail currents by 24 ± 5%. Both the isoprenaline‐ and forskolin‐induced increases in I Kr were inhibited when calcium entry was reduced by block of I Ca with nifedipine or when myocytes were pre‐incubated in BAPTA‐AM. The selective PKA inhibitor KT5720 prevented the isoprenaline‐induced increase in I Kr only when the increase in I Ca was also suppressed. These data show a novel mechanism of regulation of I Kr by PKC and this kinase was activated by β‐adrenoceptor stimulation. I Kr seems to be enhanced through a reduction in the C‐type inactivation which underlies the rectification of the channel and such a mechanism may occur in other channels with this type of inactivation.