title: Protein kinase C-mediated down-regulation of voltage-dependent sodium channels in adrenal chromaffin cells.
abstract: Treatment of cultured bovine adrenal chromaffin cells with 12-O-tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C (PKC), decreased [3H]saxitoxin ([3H]STX) binding in a concentration (IC50 = 19 nM)- and time (t1/2 = 4.5 h)-dependent manner. TPA (100 nM for 15 h) lowered the Bmax of [3H]STX binding by 53% without altering the KD value. Phorbol 12,13-dibutyrate (PDBu) also reduced [3H]STX binding, whereas 4 alpha-TPA, an inactive analogue, had no effect. The inhibitory effect of TPA was abolished when H-7 (an inhibitor of PKC), but not H-89 (an inhibitor of cyclic AMP-dependent protein kinase), was included in the culture medium for 1 h before and during TPA treatment. Simultaneous treatment with TPA in combination with either actinomycin D or cycloheximide, an inhibitor of protein synthesis, nullified the effect of TPA. TPA treatment also attenuated veratridine-induced 22Na+ influx but did not alter the affinity of veratridine for Na channels as well as an allosteric potentiation of veratridine-induced 22Na+ influx by brevetoxin. These results suggest that an activation of PKC down-regulates the density of Na channels without altering their pharmacological features; this down-regulation is mediated via the de novo synthesis of an as yet unidentified protein(s), rather than an immediate effect of Na channel phosphorylation.
authors.affiliation: Department of Pharmacology, Miyazaki Medical College, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yanagita
authors.forename: A
authors.initials: A
authors.lastname: Wada
authors.forename: R
authors.initials: R
authors.lastname: Yamamoto
authors.forename: H
authors.initials: H
authors.lastname: Kobayashi
authors.forename: T
authors.initials: T
authors.lastname: Yuhi
authors.forename: M
authors.initials: M
authors.lastname: Urabe
authors.forename: H
authors.initials: H
authors.lastname: Niina
mesh_terms: D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D015536:Down-Regulation; D004594:Electrophysiology; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012530:Saxitoxin / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology
chemical_list: D010703:Phorbol Esters; D011500:Protein Synthesis Inhibitors; D015222:Sodium Channels; D012530:Saxitoxin; D014701:Veratridine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate