title: Secretagogue-responsive and -unresponsive pools of phosphatidylinositol in pancreatic islets.
abstract: The effect of glucose on phosphatidylinositol turnover was studied. Phosphatidylinositol of rat pancreatic islets was labeled with myo[2-3H]inositol in the presence of various secretagogues (16.7 mM D-glucose, 22 mM D-mannose, 20 mM D-glyceraldehyde) and nonsecretagogues (3.3 mM D-glucose, 20 mM pyruvate, 16.7 mM D-galactose, 16.7 mM L-glucose). Upon subsequent stimulation with 16.7 mM D-glucose, only the islets that were labeled in the presence of secretagogues showed a loss of radioactivity from phosphatidylinositol. No loss of radioactivity from phosphatidylinositol occurred in the presence of 3.3 mM D-glucose even after labeling in the presence of secretagogues. A comparison of the subcellular distribution of labeled phosphatidylinositol in islets before and after stimulation with insulinotropic glucose revealed a loss of radioactivity from the plasma membrane fraction as judged by subcellular fractionation with a sucrose gradient. These results support a hypothesis advanced previously that pancreatic islets contain a unique pool of phosphatidylinositol that undergoes rapid turnover only in the presence of insulinotropic concentrations of D-glucose or other secretagogues [R. S. Rana, R. J. Mertz, A. Kowlura, J. F. Dixon, L. E. Hokin, and M. J. MacDonald (1985) J. Biol. Chem. 260, 7861-7867]. On the basis of the subcellular fractionation studies reported here, the secretagogue-responsive phosphatidylinositol pool appears to be located primarily in the plasma membrane of pancreatic islets.
mesh_terms: D000818:Animals; D002499:Centrifugation, Density Gradient; D005947:Glucose / Q000494:pharmacology; D066298:In Vitro Techniques; D007294:Inositol / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D010716:Phosphatidylinositols; D007294:Inositol; D005947:Glucose