ATP-sensitive K+ channel-dependent regulation of glucagon release and electrical activity by glucose in wild-type and SUR1-/- mouse alpha-cells.

Patch-clamp recordings and glucagon release measurements were combined to determine the role of plasma membrane ATP-sensitive K+ channels (KATP channels) in the control of glucagon secretion from mouse pancreatic alpha-cells. In wild-type mouse islets, glucose produced a concentration-dependent (half-maximal inhibitory concentration [IC50]=2.5 mmol/l) reduction of glucagon release.

The imidazoline NNC77-0020 affects glucose-dependent insulin, glucagon and somatostatin secretion in mouse pancreatic islets.

The effect of the novel imidazoline compound 2-[2-(4,5-dihydro-1H-imidazol-2-yl)-1-(5-methyl-2,3-dihydrobenzofuran-7-yl)-ethyl]-pyridine (NNC77-0020) on stimulus-secretion coupling and hormone secretion was investigated in mouse pancreatic islets and isolated alpha- and beta-cells. In the presence of elevated glucose concentrations NNC77-0020 stimulated insulin secretion concentration dependently (EC(50) 64 nM) by 200% without affecting the whole-cell K(+) current or cytoplasmic Ca(2+) levels. Capacitance measurements in single mouse beta-cells showed that intracellular application of NNC77-0020 via the recording pipette enhanced Ca(2+)-dependent exocytosis.

Rapid association of protein kinase C-epsilon with insulin granules is essential for insulin exocytosis.

Glucose-dependent exocytosis of insulin requires activation of protein kinase C (PKC). However, because of the great variety of isoforms and their ubiquitous distribution within the beta-cell, it is difficult to predict the importance of a particular isoform and its mode of action. Previous data revealed that two PKC isoforms (alpha and epsilon) translocate to membranes in response to glucose (Zaitzev, S.

Involvement of protein kinase C-epsilon in inositol hexakisphosphate-induced exocytosis in mouse pancreatic beta-cells.

Inositolhexakisphosphate (InsP6) plays a pivotal role in the pancreatic beta-cell stimulus-secretion coupling. We have used capacitance measurements to study the effects of InsP6 on Ca2+-dependent exocytosis in single mouse pancreatic beta-cells. In the presence of inhibitors of the protein phosphatase calcineurin to block endocytosis, intracellular application of InsP6 produced a dose-dependent stimulation of exocytosis, and half-maximal effect was observed at 22 microM.

Phosphatidylinositol 4-kinase serves as a metabolic sensor and regulates priming of secretory granules in pancreatic beta cells.

Insulin secretion is controlled by the beta cell's metabolic state, and the ability of the secretory granules to undergo exocytosis increases during glucose stimulation in a membrane potential-independent fashion. Here, we demonstrate that exocytosis of insulin-containing secretory granules depends on phosphatidylinositol 4-kinase (PI 4-kinase) activity and that inhibition of this enzyme suppresses glucose-stimulated insulin secretion. Intracellular application of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P(2)] stimulated exocytosis by promoting the priming of secretory granules for release and increasing the number of granules residing in a readily releasable pool.

Imidazoline NNC77-0074 stimulates Ca2+-evoked exocytosis in INS-1E cells by a phospholipase A2-dependent mechanism.

We have previously demonstrated that the novel imidazoline compound (+)-2-(2-(4,5-dihydro-1H-imidazol-2-yl)-thiopene-2-yl-ethyl)-pyridine (NNC77-0074) increases insulin secretion from pancreatic beta-cells by stimulation of Ca(2+)-dependent exocytosis. Using capacitance measurements, we now show that NNC77-0074 stimulates exocytosis in clonal INS-1E cells. NNC77-0074-stimulated exocytosis was antagonised by the cytoplasmic phospholipase A(2) (cPLA(2)) inhibitors ACA and AACOCF(3) and in cells treated with antisense oligonucleotide against cPLA(2)alpha.

Imidazoline NNC77-0074 stimulates insulin secretion and inhibits glucagon release by control of Ca(2+)-dependent exocytosis in pancreatic alpha- and beta-cells.

We have investigated the effects of the novel imidazoline compound (+)-2-(2-(4,5-dihydro-1H-imidazol-2-yl)-thiopene-2-yl-ethyl)-pyridine (NNC77-0074) on stimulus-secretion coupling in isolated pancreatic alpha- and beta-cells. NNC77-0074 stimulated glucose-dependent insulin secretion in intact mouse pancreatic islets. No effect was observed at View Article and Find Full Text PDF

cPLA2alpha-evoked formation of arachidonic acid and lysophospholipids is required for exocytosis in mouse pancreatic beta-cells.

Using capacitance measurements, we investigated the effects of intracellularly applied recombinant human cytosolic phospholipase A2 (cPLA2alpha) and its lipolytic products arachidonic acid and lysophosphatidylcholine on Ca2+-dependent exocytosis in single mouse pancreatic beta-cells. cPLA2alpha dose dependently (EC50 = 86 nM) stimulated depolarization-evoked exocytosis by 450% without affecting the whole cell Ca2+ current or cytoplasmic Ca2+ levels. The stimulatory effect involved priming of secretory granules as reflected by an increase in the size of the readily releasable pool of granules from 70-80 to 280-300.

Increase in cellular glutamate levels stimulates exocytosis in pancreatic beta-cells.

Glutamate has been implicated as an intracellular messenger in the regulation of insulin secretion in response to glucose. Here we demonstrate by measurements of cell capacitance in rat pancreatic beta-cells that glutamate (1 mM) enhanced Ca2+-dependent exocytosis. Glutamate (1 mM) also stimulated insulin secretion from permeabilized rat beta-cells.

Sulfonylurea receptor type 1 knock-out mice have intact feeding-stimulated insulin secretion despite marked impairment in their response to glucose.

The ATP-sensitive potassium channel is a key molecular complex for glucose-stimulated insulin secretion in pancreatic beta cells. In humans, mutations in either of the two subunits for this channel, the sulfonylurea type 1 receptor (Sur1) or Kir6.2, cause persistent hyperinsulinemic hypoglycemia of infancy.

Sulfatide controls insulin secretion by modulation of ATP-sensitive K(+)-channel activity and Ca(2+)-dependent exocytosis in rat pancreatic beta-cells.

The glycosphingolipid sulfatide is present in secretory granules and at the surface of pancreatic beta-cells, and antisulfatide antibodies (ASA; IgG1) are found in serum from the majority of patients with newly diagnosed type 1 diabetes. Here we demonstrate that sulfatide produced a glucose- and concentration-dependent inhibition of insulin release from isolated rat pancreatic islets. This inhibition of insulin secretion was due to activation of ATP-sensitive K(+)-(K(ATP)) channels in single rat beta-cells.

Nateglinide, but not repaglinide, stimulates growth hormone release in rat pituitary cells by inhibition of K channels and stimulation of cyclic AMP-dependent exocytosis.

Objective: GH causes insulin resistance, impairs glycemic control and increases the risk of vascular diabetic complications. Sulphonylureas stimulate GH secretion and this study was undertaken to investigate the possible stimulatory effect of repaglinide and nateglinide, two novel oral glucose regulators, on critical steps of the stimulus-secretion coupling in single rat somatotrophs.

Methods: Patch-clamp techniques were used to record whole-cell ATP-sensitive K(+) (K(ATP)) and delayed outward K(+) currents, membrane potential and Ca(2+)-dependent exocytosis.

Inositol hexakisphosphate promotes dynamin I- mediated endocytosis.

Membrane homeostasis is maintained by exocytosis and endocytosis. The molecular mechanisms regulating the interplay between these two processes are not clear. Inositol hexakisphosphate (InsP(6)) is under metabolic control and serves as a signal in the pancreatic beta cell stimulus-secretion coupling by increasing Ca(2+)-channel activity and insulin exocytosis.