Pertussis toxin inhibits norepinephrine-stimulated inositol phosphate formation in primary brain cell cultures.
Norepinephrine (NE) increased formation of [3H]inositol phosphates ( [3H]InsPs) in primary cultures of neuronal and glial cells from 1-day-old rat brain. This response appeared to be mediated by alpha 1-adrenergic receptors, because prazosin was 40-fold more potent than yohimbine in blocking it. Pretreatment with pertussis toxin (PTX) dose-dependently decreased this response by 70-80%. The IC50 for PTX (7 ng/ml) was similar to that for blocking of alpha 2-adrenergic receptor-mediated decreases in cyclic AMP accumulation in the same cells. PTX pretreatment caused only a small, not statistically significant, inhibition of the [3H]InsP response to the muscarinic cholinergic receptor agonist carbachol in these cells. Radioligand binding studies showed that both neuronal and glial cultures contained mixed populations of alpha 1a- and alpha 1b-adrenergic receptor subtypes. Selective inactivation of the alpha 1b population by chloroethylclonidine reduced NE-stimulated [3H]InsP formation by 25 +/- 6%. Pretreatment with both PTX and chloroethylclonidine caused additive decreases (90 +/- 3%) in the NE response. NE-stimulated [3H]InsP formation was partially dependent on extracellular calcium, because it was decreased 64 +/- 6% by removal of calcium and 56 +/- 13% by addition of 1 mM CdCl2, although it was not affected by 1 microM nifedipine. These results suggest that NE stimulates [3H]InsP formation in neuronal and glial cultures through a pertussis toxin-sensitive guanine nucleotide-binding protein. This response appears to be mediated primarily by the alpha 1a subtype and may be subsequent to calcium influx.
Wilson
K M
KM
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322.
Minneman
K P
KP
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002217:Carbachol / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004146:Dioxanes / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism*; D009638:Norepinephrine / Q000037:antagonists & inhibitors*; D037342:Pertussis Toxin; D010627:Phenethylamines / Q000378:metabolism; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D044024:Tetralones; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
D004146:Dioxanes; D007295:Inositol Phosphates; D010627:Phenethylamines; D011942:Receptors, Adrenergic, alpha; D044024:Tetralones; D010566:Virulence Factors, Bordetella; D015016:Yohimbine; C051731:chlorethylclonidine; C010652:BE 2254; D002217:Carbachol; D000242:Cyclic AMP; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D003000:Clonidine; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin