Relationship between hormonal activation of phosphatidylinositol hydrolysis, fluid secretion and calcium flux in the blowfly salivary gland.
The addition of 5-hydroxytryptamine to the isolated blowfly salivary gland stimulates fluid secretion, transepithelial calcium transport and the breakdown of 32P- or 3H-labelled phosphatidylinositol The breakdown of [32P]phosphatidylcholine and [32P]-phosphatidylethanolamine was not stimulated by 5-hydroxytryptamine. In salivary glands incubated with myo-[2-3H]inositol for 1--3 h, more than 95% of the label retained by the tissue was in the form of phosphatidylinositol. The addition of 5-hydroxytryptamine resulted in an increase in the accumulation of label in intracellular inositol 1:2-cyclic phosphate, inositol 1-phosphate and free inositol along with an increase in the release of [3H]inositol to the medium and saliva. The release of [3H]inositol to the medium served as a sensitive indicator of phosphatidylinositol breakdown. The release of [3H]inositol was not increased by cyclic AMP or the bivalent-cation ionophore A23187 under conditions in which salivary secretion was accelerated. The stimulation of fluid secretion by low concentrations of 5-hydroxytryptamine was potentiated by 3-isobutyl-1-methylxanthine, which had no effect on inositol release. The stimulation of fluid secretion by 5-hydroxytryptamine was greatly reduced in calcium-free buffer, but the breakdown of phosphatidylinositol continued at the same rate in the absence of calcium. These results support the hypothesis that breakdown of phosphatidylinositol by 5-hydroxytryptamine is involved in the gating of calcium.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D004175:Diptera / Q000378:metabolism*; D005260:Female; D006868:Hydrolysis; D066298:In Vitro Techniques; D007294:Inositol / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D012469:Salivary Glands / Q000187:drug effects / Q000378:metabolism*; D012636:Secretory Rate / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*
D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D010743:Phospholipids; D012701:Serotonin; D007294:Inositol; D000242:Cyclic AMP; D002118:Calcium