title: Dual mechanism involved in the hydrolysis of polyphosphoinositides in rat pancreatic islets.
abstract: We investigated insulin secretion and inositol phosphate formation in intact and permeabilized rat pancreatic islets, the objective being to elucidate mechanisms of activation of phospholipase-C in pancreatic islets. The intact islets prelabeled with myo-[3H]inositol were incubated in Krebs-Ringer bicarbonate buffer containing 10 mM LiCl and 1 mM myoinositol. Glucose, alpha-ketoisocaproate (KIC), and sulfated cholecystokinin (CCK8S) increased insulin secretion and formation of [3H]inositol phosphate, [3H]inositol bisphosphate, and [3H] inositol trisphosphate. Mannoheptulose, a glucokinase inhibitor, inhibited glucose-induced insulin secretion and [3H]inositol phosphate formation; however, it did not inhibit KIC- and CCK8S-induced secretion and formation. Both glucose- and KIC-induced insulin secretion and [3H]inositol phosphate formation were blocked by 2,4-dinitrophenol, an uncoupler of oxidative phosphorylation in the mitochondria. The islets prelabeled with myo-[3H]inositol were permeabilized by digitonin and then incubated in intracellular mimicking medium containing 1 microM Ca2+ and 2.5 mM ATP. Glucose had no effect on [3H]inositol phosphate formation in the permeabilized islets, and CCK8S increased the formation of [3H]inositol phosphates. Thus, phospholipase-C in pancreatic islets is activated not only via ligand-receptor interaction in the plasma membrane in the case of hormone stimulation, but also by metabolic product(s) in the case of fuel stimulation.
authors.affiliation: Second Department of Internal Medicine, Chiba University School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: A
authors.initials: A
authors.lastname: Kanatsuka
authors.forename: H
authors.initials: H
authors.lastname: Makino
authors.forename: H
authors.initials: H
authors.lastname: Ohsawa
authors.forename: S
authors.initials: S
authors.lastname: Yoshida
mesh_terms: D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects; D004072:Digitonin / Q000493:pharmacokinetics; D006868:Hydrolysis; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D004072:Digitonin