Further characterization of 5-HT- and 5-HT3 receptor agonists'-stimulated phosphoinositol phosphates accumulation.
The calcium requirement for serotonin (5-HT)- and the 5-HT3 receptor agonists, 2-Me-5-HT- and PBG-dependent breakdown of phosphatidyl inositol has been examined in the rat fronto-cingulate cortex. The omission of added Ca2+ from the Kreb's incubation medium reduced the [3H]inositol phosphate accumulation from pre-labelled phospholipids. Removal of Ca2+ by pre-incubation with EGTA (0.5 mM), as well as the addition of the calcium channel blocker, lanthanum (10 microM), abolished the 5-HT- and the 5-HT3 receptor agonists'-stimulated phosphoinositide (PI) response. By contrast, the calcium ionophores, A 23187 and Ionomycin (both at 30 microM) stimulated PI hydrolysis, and this effect was additive to the increased PI turnover induced by 5-HT, 2-Me-5-HT and PBG. The increase in phosphoinositide hydrolysis induced by 5-HT and 2-Me-5-HT was significantly inhibited by phorbol dibutyrate (PDBu) and phorbol myristate acetate, indicating that the activation of protein kinase C (PKC) may provide negative feedback to the PI response induced by 5-HT and 2-Me-5-HT-stimulated PI metabolism was reversed by the PKC inhibitors, staurosporine, calphostin C and chelerythrine (all at 10 microM), however, Pertussis toxin (0.5 and 1 microgram) had no effect on either 5-HT's or 2-Me-5-HT's increased stimulation of PI hydrolysis, suggesting that this response is not associated to a Gi GTP binding protein.
Department of Pharmacology and Toxicology, University of Maryland, Baltimore 21201.
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Edwards
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Ashby
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Wang
D000818:Animals; D019204:GTP-Binding Proteins / Q000187:drug effects; D007295:Inositol Phosphates / Q000378:metabolism*; D008297:Male; D037342:Pertussis Toxin; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010704:Phorbols / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000187:drug effects*; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007295:Inositol Phosphates; D010704:Phorbols; D010716:Phosphatidylinositols; D011985:Receptors, Serotonin; D010566:Virulence Factors, Bordetella; D012701:Serotonin; D015240:Phorbol 12,13-Dibutyrate; C045918:2-methyl-5-HT; D037342:Pertussis Toxin; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate; C033085:phorbol