title: Receptor-mediated net breakdown of phosphatidylinositol 4,5-bisphosphate in parotid acinar cells.
abstract: The metabolism of phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] in rat parotid acinar cells was investigated, particularly with regard to the effects of receptor-active agonists. Stimulation of cholinergic-muscarinic receptors with methacholine provoked a rapid disappearance of 40--50% of [32P]PtdIns(4,5)P2, but had no effect on PtdIns4P. Adrenaline, acting on alpha-adrenoceptors, and Substance P also stimulated net loss of PtdIns(4,5)P2. The beta-adrenoceptor agonist, isoprenaline, and the Ca2+ ionophore, ionomycin, failed to affect labelled PtdIns(4,5)P2 or PtdIns4P. By chelation of extracellular Ca2+ with excess EGTA, and by an experimental protocol that eliminates cellular Ca2+ release, it was demonstrated that the agonist-induced decrease in PtdIns(4,5)P2 is independent of both Ca2+ influx and Ca2+ release. These results may suggest that net PtdIns(4,5)P2 breakdown is an early event in the stimulus-response pathway of the parotid acinar cell and could be directly involved in the mechanism of agonist-induced Ca2+ release from the plasma membrane.
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D010306:Parotid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols / Q000378:metabolism*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011950:Receptors, Cholinergic / Q000187:drug effects; D013373:Substance P / Q000494:pharmacology
chemical_list: D008688:Methacholine Compounds; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D011950:Receptors, Cholinergic; D016210:Methacholine Chloride; D013373:Substance P; D001285:Atropine; D011433:Propranolol; D002118:Calcium; D004837:Epinephrine