title: Relationship between phosphatidylinositol synthesis and recovery of 5-hydroxytryptamine-responsive Ca2+ flux in blowfly salivary glands.
abstract: Each salivary gland contains about 135 pmol of phosphatidylinositol. In glands prelabelled by incubation for 1 h with [32P]Pi or [3H]inositol there was a subsequent breakdown of 80% of the labelled phosphatidylinositol over a 2 h incubation period with 10 micrometer-5-hydroxytryptamine. However, there was no detectable decrease either in total phosphatidylinositol based on phosphorus analysis by chemical estimation or in the radioactivity of [32P]phosphatidylinositol in salivary glands of flies raised from the larval stage on diets containing[32P]Pi and whose phospholipids were uniformly labelled. These results suggest that the pool of phosphatidylinositol involved with Ca2+ gating is a small fraction of the total phosphatidylinositol content. Furthermore it is this small compartment that is preferentially radioactively labelled during short-term incubations with radioactively labelled precursors. In salivary glands incubated for 2 h with 10 micrometer-5-hydroxytryptamine there was a marked decrease in the flux of 45Ca2+ across the gland. After removal of the hormone, incubation of salivary glands for 1 h in the presence of 2mM-inositol, but not choline or ethanolamine, resulted in a recovery of hormone-responsive 45Ca2+ flux. Quantitative studies revealed that less than 9 pmol of phosphatidylinositol must be formed to fully restoret he 5-hydroxytryptamine-responsive 45Ca2+ flux.
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002794:Choline / Q000378:metabolism; D004175:Diptera / Q000378:metabolism*; D004983:Ethanolamines / Q000378:metabolism; D066298:In Vitro Techniques; D007294:Inositol / Q000378:metabolism; D010716:Phosphatidylinositols / Q000096:biosynthesis*; D012469:Salivary Glands / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology*
chemical_list: D004983:Ethanolamines; D010716:Phosphatidylinositols; D012701:Serotonin; D007294:Inositol; D002794:Choline; D002118:Calcium