Inhibition of Ca2+-dependent K+ channels in rat carotid body type I cells by protein kinase C.
1. Whole-cell patch clamp recordings were used to investigate the effects of protein kinase C (PKC) activation on K+ and Ca2+ currents in type I cells isolated from the rat carotid body. 2. Pretreatment of cells for 10 min at 37 C with 4alpha-phorbol 12,13-didecanoate (4alpha-PDD, 200 nM), a phorbol ester which does not activate PKC, did not affect K+ current density as compared with cells pretreated with vehicle alone. By contrast, identical pretreatment with 200 nM 12-O-teradecanoylphorbol-13-acetate (TPA, a PKC activator) dramatically reduced K+ current density in type I cells. This effect was prevented by co-incubation of cells with the PKC inhibitor bisindolylmaleimide (BIM, 3 microM). 3. The sensitivity of K+ currents to inhibition by 200 microM Cd2+ (indicative of the presence of Ca2+-dependent K+ channels) was markedly reduced in TPA-treated cells as compared with sham-treated cells, cells treated with 4alpha-PDD, and cells treated with both TPA and BIM. Cd2+-resistant K+ current densities were of similar magnitude in all four groups of cells, as were the input resistances determined over the voltage range -100 mV to -50 mV. 4. Ca2+ channel current density was not significantly different in type I cells pretreated with 200 nM 4alpha-PDD as compared with cells treated with the same concentration of TPA. 5. The degree of inhibition of K+ currents caused by hypoxia (Po2 15-20 mmHg) was unaltered by pretreatment of cells with 3 microM BIM. 6. The resting membrane potential of cells pretreated with TPA was depolarized as compared with controls, and the Ca2+-dependent K+ channel inhibitor iberiotoxin (20 nM) failed to depolarize these cells further. 7. Our results suggest that activation of PKC causes a marked, selective inhibition of Ca2+-dependent K+ currents in type I carotid body cells, but that PKC activation is unlikely to account for inhibition of these channels by acute hypoxia.
Institute for Cardiovascular Research, University of Leeds, Leeds LS2 9JT, UK. c.s.peers@leeds.ac.uk
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D000818:Animals; D002118:Calcium / Q000502:physiology*; D002344:Carotid Body / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008301:Maleimides / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010703:Phorbol Esters / Q000494:pharmacology; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D010703:Phorbol Esters; D026902:Potassium Channel Blockers; D015221:Potassium Channels; C008876:phorbol-12,13-didecanoate; D011493:Protein Kinase C; C088060:bisindolylmaleimide; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium