Second messengers involved in genetic regulation of the number of calcium channels in bovine adrenal chromaffin cells in culture.
Bovine adrenal chromaffin cells in culture show an increased formation of [3H]inositol phosphates (after preloading with [3H]inositol) on depolarisation with increased extracellular K+. This increased breakdown of inositol lipid is further increased by the dihydropyridine Ca2+ channel activator BAY K 8644 at nM concentrations, implying that proteins which bind dihydropyridines are involved in this mechanism. Further, pretreatment of adrenal cells with pertussis toxin (100 ng ml-1) prevented the K(+)-induced breakdown of inositol lipids, arguing the involvement of a pertussis toxin-sensitive G protein in the effect. Chronic exposure of bovine adrenal chromaffin cells to a concentration of ethanol which inhibits K(+)-induced breakdown of inositol phospholipid, caused a 70-100% increase in the binding of [3H]DHP sites. In these experiments it was found that excess extracellular Ca2+ would considerably reduce this up-regulation, whereas growth of cells in pertussis toxin closely mimicked the up-regulation obtained by growth of cells in ethanol. These experiments suggest that inhibition of membrane Ca2+ flux, through a G protein-associated channel, is closely involved in the ethanol-induced regulation of [3H]dihydropyridine binding sites. The inositol lipid-protein kinase C second messenger system is also implicated in this regulation, by experiments in which inhibitors of protein kinase C (chronic treatment with phorbol myristyl acetate, or with sphingosine) up-regulated binding sites for [3H]dihydropyridine to a similar extent as that seen with growth in ethanol.
Division of Biomedical Sciences, King's College, Strand, London, U.K.
C H
CH
Brennan
J M
JM
Littleton
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000187:drug effects / Q000378:metabolism*; D004095:Dihydropyridines / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D007295:Inositol Phosphates / Q000378:metabolism; D007700:Kinetics; D037342:Pertussis Toxin; D010703:Phorbol Esters / Q000494:pharmacology; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology*; D015854:Up-Regulation / Q000187:drug effects; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015220:Calcium Channels; D004095:Dihydropyridines; D007295:Inositol Phosphates; D010703:Phorbol Esters; D010566:Virulence Factors, Bordetella; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; D037342:Pertussis Toxin