Functional effects of protein kinase C activation on the human cardiac Na+ channel.
The cardiac Na+ current plays an important role in determining normal and abnormal impulse propagation in the heart. We have investigated the effects of protein kinase C (PKC) activation on the recombinant human cardiac Na+ channel (hH1) following heterologous expression in Xenopus laevis oocytes. Phorbol 12-myristate 13-acetate (PMA), which directly activates PKC, reduced current amplitude at all test potentials (43 +/- 12% at -10 mV). In contrast to the rat brain IIA (rBIIA) channel, there was no apparent change in either macroscopic Na+ current decay or the voltage dependence of channel gating. Further experiments indicate that the effects of PMA were mediated by PKC activation: (1) an inactive stereoisomer, 4 alpha-PMA, had no effect; (2) preincubation with the protein kinase inhibitor chelerythrine prevented the PMA effects; and (3) a hydrolyzable diacylglycerol analogue, 1-oleoyl-2-acetyl-glycerol, also reduced current (22 +/- 5%). In addition, when the alpha 1B-adrenergic receptor was coexpressed with hH1, the alpha-receptor agonist methoxamine reduced hH1 current (45 +/- 10%), an effect that could be eliminated by chelerythrine preincubation. When a conserved consensus PKC site (serine 1503) in the III-IV interdomain linker thought to be responsible for the PKC effects on rBIIA was mutated, PMA still reduced Na+ current, but the magnitude of the effect was smaller compared with that for the wild-type channel. Similar findings were obtained with alpha 1-receptor stimulation following receptor coexpression with the mutant channel. We conclude that activation of PKC modulates the human cardiac Na+ channel by at least two mechanisms, one similar to that seen with rat brain channels, involving a conserved putative PKC site, and a second more specific to the cardiac isoform.
Murray
K T
KT
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tenn. 37232-6602, USA. kathy.murray@mcmail.vanderbilt.edu
Hu
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Daw
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JR
Shin
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Watson
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Mashburn
A B
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George
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D000470:Alkaloids; D000818:Animals; D053119:Benzophenanthridines; D006224:Cricetinae; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008729:Methoxamine / Q000494:pharmacology; D009154:Mutation; D009206:Myocardium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010617:Phenanthridines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000031:analogs & derivatives / Q000494:pharmacology; D014162:Transfection; D014982:Xenopus laevis
D000470:Alkaloids; D053119:Benzophenanthridines; D004075:Diglycerides; D010617:Phenanthridines; D018340:Receptors, Adrenergic, alpha-1; D015222:Sodium Channels; C038237:1-oleoyl-2-acetylglycerol; C016299:chelerythrine; D011493:Protein Kinase C; D008729:Methoxamine; D013755:Tetradecanoylphorbol Acetate