title: Activation of protein kinase C reduces L-type calcium channel activity of GH3 pituitary cells.
abstract: These studies describe the effect of protein kinase C (PKC) activation on the activity of voltage-sensitive L-type Ca2+ channels of GH3 pituitary cells. The rate of 45Ca2+ uptake was stimulated greater than 25-fold by depolarization in the presence of BAY K 8644; the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) reduced this response by 70% in a concentration-dependent fashion. Phorbol 12,13-dibutyrate (PDBu) inhibited depolarization-induced 45Ca2+ uptake within 1 min and caused a nearly maximal reduction after 1 h; its effects were rapidly reversible. TPA decreased the high K(+)-stimulated increase in intracellular free calcium ion concentration ([Ca2+]i) from 8.5- to 3.2-fold by 5 min and to 2.0-fold after 18 h without altering the peak [Ca2+]i response to the peptide hormone TRH. Ca2+ channel current, measured directly using the whole cell configuration of the patch-clamp technique, declined an average of 6.4% over 5 min for control cells and 28.9% when TPA was added to the bathing medium for 5 min. Treatment with 100 nM TPA for 24 h dramatically reduced peak current without shifting the peak of the current-voltage relationship. The mean peak Ca2+ channel current was reduced from 423 to 128 pA, although a few cells seemed completely resistant. To determine whether the effects of phorbol esters were due to the activation of PKC we tested the potency of several drugs to inhibit L-channel activity and to shift the affinity of the epidermal growth factor (EGF) receptor, an established PKC response.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology, University of Rochester School of Medicine and Dentistry, New York 14642.
authors.forename: A A
authors.initials: AA
authors.lastname: Haymes
authors.forename: Y W
authors.initials: YW
authors.lastname: Kwan
authors.forename: J P
authors.initials: JP
authors.lastname: Arena
authors.forename: R S
authors.initials: RS
authors.lastname: Kass
authors.forename: P M
authors.initials: PM
authors.lastname: Hinkle
mesh_terms: D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics; D015220:Calcium Channels / Q000378:metabolism* / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology; D004594:Electrophysiology; D004789:Enzyme Activation; D009994:Osmolar Concentration; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010911:Pituitary Neoplasms / Q000378:metabolism* / Q000473:pathology; D011493:Protein Kinase C / Q000172:deficiency / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D015220:Calcium Channels; D015240:Phorbol 12,13-Dibutyrate; D013973:Thyrotropin-Releasing Hormone; D000242:Cyclic AMP; D011493:Protein Kinase C; D002118:Calcium