title: Carbachol induces a rapid and sustained hydrolysis of polyphosphoinositide in bovine tracheal smooth muscle measurements of the mass of polyphosphoinositides, 1,2-diacylglycerol, and phosphatidic acid.
abstract: The effects of carbachol on polyphosphoinositides and 1,2-diacylglycerol metabolism were investigated in bovine tracheal smooth muscle by measuring both lipid mass and the turnover of [3H]inositol-labeled phosphoinositides. Carbachol induces a rapid reduction in the mass of phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-monophosphate and a rapid increase in the mass of 1,2-diacylglycerol and phosphatidic acid. These changes in lipid mass are sustained for at least 60 min. The level of phosphatidylinositol shows a delayed and progressive decrease during a 60-min period of carbachol stimulation. The addition of atropine reverses these responses completely. Carbachol stimulates a rapid loss in [3H]inositol radioactivity from phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 4-monophosphate associated with production of [3H]inositol trisphosphate. The carbachol-induced change in the mass of phosphoinositides and phosphatidic acid is not affected by removal of extracellular Ca2+ and does not appear to be secondary to an increase in intracellular Ca2+. These results indicate that carbachol causes phospholipase C-mediated polyphosphoinositide breakdown, resulting in the production of inositol trisphosphate and a sustained increase in the actual content of 1,2-diacylglycerol. These results strongly suggest that carbachol-induced contraction is mediated by the hydrolysis of polyphosphoinositides with the resulting generation of two messengers: inositol 1,4,5-trisphosphate and 1,2-diacylglycerol.
mesh_terms: D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D002417:Cattle; D004075:Diglycerides / Q000378:metabolism*; D005989:Glycerides / Q000378:metabolism*; D006868:Hydrolysis; D007294:Inositol / Q000378:metabolism; D007700:Kinetics; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D014132:Trachea / Q000187:drug effects / Q000378:metabolism; D014316:Tritium
chemical_list: D004075:Diglycerides; D005989:Glycerides; D010712:Phosphatidic Acids; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D014316:Tritium; D007294:Inositol; D002217:Carbachol