Impact of biotin supplemented diet on mouse pancreatic islet β-cell mass expansion and glucose induced electrical activity.

Biotin supplemented diet (BSD) is known to enhance β-cell replication and insulin secretion in mice. Here, we first describe BSD impact on the islet β-cell membrane potential (Vm) and glucose-induced electrical activity. BALB/c female mice (n ≥ 20) were fed for nine weeks after weaning with a control diet (CD) or a BSD (100X).

The Anx7(+/-) knockout mutation alters electrical and secretory responses to Ca(2+)-mobilizing agents in pancreatic β-cells.

Insulin secretion from the pancreatic β-cell is controlled by changes in membrane potential and intracellular Ca(2+). The contribution of intracellular Ca(2+) stores to this process is poorly understood. We have previously shown that β-cells of mice lacking one copy of the Annexin 7 gene (Anx7(+/-)) express reduced levels of IP(3) receptors and defects in IP(3)-dependent Ca(2+) signaling.

Isolation of viable porcine islets by selective osmotic shock without enzymatic digestion.

Islet transplantation is a potential cure for type 1 diabetes, but clinical results have been disappointing. Currently, islet isolation is by enzymatic digestion of the pancreas which has significant pitfalls: warm ischemia exposure, collagenase-induced damage to the islet mass and viability, poor reproducibility, high cost, a relatively low number of islets obtained per whole pancreas, and selection of islets for collagenase resistance rather than for glucose responsiveness. In the present study we performed a series of experiments in a porcine model to demonstrate the feasibility of a new isolation method based on selective osmotic shock (SOS) using very high glucose solutions, doubling or tripling physiological osmotic strength.

Apoptosis is directly related to intracellular amyloid accumulation in a cell line derived from the cerebral cortex of a trisomy 16 mouse, an animal model of Down syndrome.

Human Down syndrome (DS) represents the most frequent cause of mental retardation associated to a genetic condition. DS also exhibits a characteristic early onset of neuropathology indistinguishable from that observed in Alzheimer's disease (AD), namely the deposition of the beta-amyloid peptide. Early endosomal dysfunction has been described in individuals with DS and AD, suggesting an important role of this subcellular compartment in the onset and progression of the pathology.

Ion channel formation by Alzheimer's disease amyloid beta-peptide (Abeta40) in unilamellar liposomes is determined by anionic phospholipids.

Incorporation of Alzheimer's disease amyloid beta-proteins (AbetaPs) across natural and artificial bilayer membranes leads to the formation of cation-selective channels. To study the peptide-membrane interactions involved in channel formation, we used cation reporter dyes to measure AbetaP-induced influx of Na+, Ca2+, and K+ into liposomes formed from phosphatidylserine (PS), phosphatidylinositol (PI) and phosphatidylcholine (PC). We found that Abeta40, but not Abeta40-1 or Abeta28, caused a dose-dependent increase in the concentration of each cation in the lumen of liposomes formed from the acidic phospholipids PS and PI.

Effect of glycemic index on whole-body substrate oxidation in obese women.

Background: Glycemic index is hypothesized to determine fuel partitioning through serum plasma insulin modifications induced by dietary carbohydrates, thereby modulating fat accretion or oxidation.

Objective: To assess the glycemic effects on postprandial fuel oxidation and blood response.

Design: In all, 12 obese women were fed on a randomized crossover design with two test meals (breakfast+lunch).

Proinsulin serum concentrations in women with polycystic ovary syndrome: a marker of beta-cell dysfunction?

Background: The aim of this study was to establish the effect of polycystic ovary syndrome (PCOS) adjusted for adiposity on proinsulin concentrations.

Methods: Ninety-one women with PCOS and 72 normal cycling (NC) women were recruited. A 2 h, 75 g oral glucose tolerance test was performed.

Loperamide mobilizes intracellular Ca2+ stores in insulin-secreting HIT-T15 cells.

1 We have investigated the effects of loperamide on intracellular Ca(2+) stores and membrane K(+) channels in insulin-secreting hamster insulinoma (HIT-T15) cells. 2 In cell-attached patch-clamp mode, loperamide (3-250 micro M) activated large single-channel currents. The loperamide-activated currents were tentatively identified as Ca(2+)-activated K(+) channel (K(Ca)) currents based on their single-channel conductance (145 pS), apparent reversal potential, and insensitivity to tolbutamide.

Pregnancy hormones prevent diabetes and reduce lymphocytic infiltration of islets in the NOD mouse.

Pregnancy is associated with a depression of the immune inflammatory system, and with increased growth and function of the pancreatic islets of Langerhans. We monitored glucosuria, blood glucose concentration, and lymphocytic infiltration of pancreatic islets in 30 female, 10-wk-old, pre-diabetic nonobese diabetic (NOD) mice divided into 3 treatment groups for 13 wk: group 1, saline; group 2, pregnancy hormones (dexamethasone 4 mg/Kg/day, progesterone 1.7 mg/Kg/day, growth hormone 0.

Evaluation of insulin resistance in two kinds of South American camelids: llamas and alpacas.

Insulin resistance was evaluated in South American camelids, llamas and alpacas, by use of the minimal model test and the insulin tolerance test. Animals were catheterized for long-term studies and tamed to minimize stress during evaluation. Results indicated a low insulin sensitivity index (SI) = 0 to 0.

Defects in inositol 1,4,5-trisphosphate receptor expression, Ca(2+) signaling, and insulin secretion in the anx7(+/-) knockout mouse.

The mammalian anx7 gene codes for a Ca(2+)-activated GTPase, which supports Ca(2+)/GTP-dependent secretion events and Ca(2+) channel activities in vitro and in vivo. To test whether anx7 might be involved in Ca(2+) signaling in secreting pancreatic beta cells, we knocked out the anx7 gene in the mouse and tested the insulin-secretory properties of the beta cells. The nullizygous anx7 (-/-) phenotype is lethal at embryonic day 10 because of cerebral hemorrhage.

Tetracaine stimulates insulin secretion from the pancreatic beta-cell by release of intracellular calcium.

The role of intracellular calcium stores in stimulus-secretion coupling in the pancreatic beta-cell is largely unknown. We report here that tetracaine stimulates insulin secretion from collagenase-isolated mouse islets of Langerhans in the absence of glucose or extracellular calcium. We also found that the anesthetic evokes a dose-dependent rise of the intracellular free-calcium concentration ([Ca2+]i) in cultured rat and mouse beta-cells.

Glucagon induces suppression of ATP-sensitive K+ channel activity through a Ca2+/calmodulin-dependent pathway in mouse pancreatic beta-cells.

Glucagon is known to increase intracellular cAMP levels and enhance glucose-induced electrical activity and insulin secretion in pancreatic beta-cell perfused with Krebs-Ringer bicarbonate solution. The present experiments were aimed at evaluation of the hypothesis that changes in beta-cells ATP-sensitive K+ (K(ATP)) channel activity are involved in the glucagon-induced enhancement of electrical activity. Channel activity was recorded using the cell-attached configuration of the patch-clamp technique.

Evidence that calcium release-activated current mediates the biphasic electrical activity of mouse pancreatic beta-cells.

The electrical response of pancreatic beta-cells to step increases in glucose concentration is biphasic, consisting of a prolonged depolarization with action potentials (Phase 1) followed by membrane potential oscillations known as bursts. We have proposed that the Phase 1 response results from the combined depolarizing influences of potassium channel closure and an inward, nonselective cation current (ICRAN) that activates as intracellular calcium stores empty during exposure to basal glucose (Bertram et al., 1995).

Ionic mechanisms involved in the regulation of insulin secretion by muscarinic agonists.

The effects of the muscarinic agonist oxotremorine-m (oxo-m) on insulin secretion, K(+)-permeability and electrical activity from isolated mouse pancreatic islets were studied. Oxo-m potentiated glucose-induced insulin secretion in a dose-dependent manner, saturating at ca. 10 microM.

Magnitude and modulation of pancreatic beta-cell gap junction electrical conductance in situ.

The parallel gap junction electrical conductance between a beta-cell and its nearest neighbors was measured by using an intracellular microelectrode to clamp the voltage of a beta-cell within a bursting islet of Langerhans. The holding current records consisted of bursts of inward current due to the synchronized oscillations in membrane potential of the surrounding cells. The membrane potential record of the impaled cell, obtained in current clamp mode, was used to estimate the behavior of the surrounding cells during voltage clamp, and the coupling conductance was calculated by dividing the magnitude of the current bursts by that of the voltage bursts.

A role for calcium release-activated current (CRAC) in cholinergic modulation of electrical activity in pancreatic beta-cells.

S. Bordin and colleagues have proposed that the depolarizing effects of acetylcholine and other muscarinic agonists on pancreatic beta-cells are mediated by a calcium release-activated current (CRAC). We support this hypothesis with additional data, and present a theoretical model which accounts for most known data on muscarinic effects.

Modulatory mechanism of ACTH on insulin secretion: effect on cytosolic Ca2+, membrane potential and Ca(2+-ATPase activity.

The aim of this work was to get some insight into the mechanism by which ACTH produces its enhancing effect on glucose-induced insulin secretion. For this purpose we have determined: a) the release of insulin by isolated rat islets incubated with 3.3 or 16.

Oxotremorine-m potentiation of glucose-induced insulin release from rat islets involves M3 muscarinic receptors.

cDNAs encoding for M1 and M3 muscarinic acetylcholine (ACh) receptors were detected in rat pancreatic islet cells by polymerase chain reaction (PCR) amplification techniques. A new cholinergic agonist, oxotremorine-m (oxo-m), in the presence of glucose (5.6 mM), produced a dose-dependent potentiation of insulin secretion saturating at approximately 5 microM.

Single-microelectrode voltage clamp measurements of pancreatic beta-cell membrane ionic currents in situ.

A conventional patch clamp amplifier was used to test the feasibility of measuring whole-cell ionic currents under voltage clamp conditions from beta-cells in intact mouse islets of Langerhans perifused with bicarbonate Krebs buffer at 37 degrees C. Cells impaled with a high resistance microelectrode (ca. 0.