Blockade of low and high threshold Ca2+ channels by diphenylbutylpiperidine antipsychotics linked to inhibition of prolactin gene expression.
The effects of diphenylbutylpiperidine (DPBP) antipsychotics on Ca2+ currents and prolactin (PRL) synthesis were studied in rat pituitary growth hormone (GH) cell lines (GH3 and GH4C1). In whole-cell patch-clamp experiments, DPBPs including fluspirilene, penfluridol, and pimozide at concentrations ranging from 0.25 to 5 microM each blocked current through low threshold T-type as well as high threshold L-type channels. Each of the drugs preferentially blocked T-type current, and complete inhibition was observed at concentrations as low as 1 microM. Inhibition of L-type channels by DPBPS was enhanced at depolarized holding potentials and promoted by prolonged channel activation. At concentrations similar to those which blocked Ca2+ currents, each of the three DPBPs markedly reduced basal PRL production by GH cells. PRL synthesis stimulated by the dihydropyridine Ca2+ agonist R5417 or thyrotropin releasing hormone (TRH) was also inhibited. The inhibitory effects of the DPBPs were observed at the level of gene transcription. Penfluridol and fluspirilene inhibited basal, Ca2(+)- and TRH-stimulated expression of a fusion gene construct containing the 5'-flanking sequence of the rat PRL gene linked to the luciferase gene. The effect was concentration-dependent with the IC50 values for both drugs of less than 1 microM. Nimodipine also reduced basal, R5417, and TRH-stimulated expression of the reporter gene construct. Similar results were obtained with a reporter gene construct containing the 5'-flanking sequence of the rat GH gene. The GH luciferase construct was only slightly responsive to R5417 and TRH; however, these responses were reduced by fluspirilene and nimodipine at concentrations of less than 1 microM. These studies demonstrate that the DPBP antipsychotics block T- as well as L-type Ca2+ channels in GH cells and inhibit PRL production at the level of transcription. They also indicate that functioning Ca2+ channels are necessary for TRH-stimulated PRL gene transcription.
Enyeart
J J
JJ
Department of Pharmacology, Ohio State University, Columbus 43210-1239.
Biagi
B A
BA
Day
R N
RN
Sheu
S S
SS
Maurer
R A
RA
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D005484:Fluspirilene / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects*; D007700:Kinetics; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects; D010395:Penfluridol / Q000494:pharmacology*; D010868:Pimozide / Q000494:pharmacology*; D010880:Piperidines / Q000494:pharmacology*; D010911:Pituitary Neoplasms; D011388:Prolactin / Q000096:biosynthesis / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D013141:Spiro Compounds / Q000494:pharmacology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology
D015220:Calcium Channels; D010880:Piperidines; D011993:Recombinant Fusion Proteins; D013141:Spiro Compounds; D010868:Pimozide; D010395:Penfluridol; D013973:Thyrotropin-Releasing Hormone; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D011388:Prolactin; D005484:Fluspirilene; D008156:Luciferases