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.
Peers
C
C
Institute for Cardiovascular Research, University of Leeds, Leeds LS2 9JT, UK. c.s.peers@leeds.ac.uk
Carpenter
E
E
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