Somatostatin promotes glucose generation of Caoscillations in pancreatic islets both in the absence and presence of tolbutamide.

Many cellular processes, including pulsatile release of insulin, are triggered by increase of cytoplasmic Ca. This study examines how somatostatin affects glucose generation of cytoplasmic Ca oscillations in mouse islets in absence and presence of tolbutamide blockade of the K channels. Ca was measured with dual wavelength microflurometry in isolated islets loaded with the indicator Fura-2.

Sulfonylurea Blockade of KATP Channels Unmasks a Distinct Type of Glucose-Induced Ca2+ Decrease in Pancreatic β-Cells.

Objectives: This study aimed to explore how sulfonylurea blockade of KATP channels affects the early Ca signals for glucose generation of insulin release.

Methods: Cytoplasmic Ca was measured with ratiometric microfluorometry in isolated mouse islets loaded with Fura-PE3.

Results: After sulfonylurea blockade of the KATP channels (50 μM-1 mM tolbutamide or 1 μM-1 mM gliclazide), increase of glucose from 3 to 20 mM resulted in suppression of elevated Ca during a 3- to 5-minute period.

Small Mouse Islets Are Deficient in Glucagon-Producing Alpha Cells but Rich in Somatostatin-Secreting Delta Cells.

Small and big mouse islets were compared with special reference to their content of glucagon-producing α-cells and somatostatin-producing δ-cells. Areas stained for glucagon and somatostatin were measured in the largest cross section of small (diameter < 60 μm) and big (diameter > 100 μm) islets. Comparison of the areas indicated proportionally more δ- than α-cells in the small islets.

Activation of alpha adrenergic and muscarinic receptors modifies early glucose suppression of cytoplasmic Ca(2+) in pancreatic β-cells.

Elevation of glucose induces transient inhibition of insulin release by lowering cytoplasmic Ca(2+) ([Ca(2+)]i) below baseline in pancreatic β-cells. The period of [Ca(2+)]i decrease (phase 0) coincides with increased glucagon release and is therefore the starting point for antisynchronous pulses of insulin and glucagon. We now examine if activation of adrenergic α2A and muscarinic M3 receptors affects the initial [Ca(2+)]i response to increase of glucose from 3 to 20mM in β-cells situated in mouse islets.

Glucose-induced inhibition of insulin secretion.

Increase in glucose is known to elevate the concentration of cytoplasmic Ca(2+) ([Ca(2+) ]i ) in pancreatic β-cells and stimulate insulin secretion. However, rise of glucose can also lower [Ca(2+) ]i and inhibit insulin release. In the present review, we examine the mechanisms for this inhibition and highlight its importance for the healthy β-cell and the development of diabetes.

Isolated mouse islets respond to glucose with an initial peak of glucagon release followed by pulses of insulin and somatostatin in antisynchrony with glucagon.

Recent studies of isolated human islets have shown that glucose induces hormone release with repetitive pulses of insulin and somatostatin in antisynchrony with those of glucagon. Since the mouse is the most important animal model we studied the temporal relation between hormones released from mouse islets. Batches of 5-10 islets were perifused and the hormones measured with radioimmunoassay in 30s fractions.

The neurotransmitter ATP triggers Ca2+ responses promoting coordination of pancreatic islet oscillations.

Objectives: Pulsatile insulin release into the portal vein is critically dependent on entrainment of the islets in the pancreas into a common oscillatory phase. Because the pulses reflect periodic variations of the cytoplasmic Ca concentration ([Ca]i), we studied whether the neurotransmitters adenosine triphosphate (ATP) and acetylcholine promote synchronization of [Ca]i oscillations between islets lacking contact.

Methods: Medium-sized and small mouse islets and cell aggregates were used for measuring [Ca]i with the indicator fura-2.

Glucose generates coincident insulin and somatostatin pulses and antisynchronous glucagon pulses from human pancreatic islets.

The kinetics of insulin, glucagon and somatostatin release was studied in human pancreatic islets. Batches of 10-15 islets were perifused and the hormones measured with RIA in 30-sec fractions. Increase of glucose from 3 to 20 mm resulted in a brief pulse of glucagon coinciding with suppression of basal insulin and somatostatin release.

Absence of adenosine A1 receptors unmasks pulses of insulin release and prolongs those of glucagon and somatostatin.

Aims: Extracellular ATP modulates pulsatile release of insulin, glucagon and somatostatin by activating P2Y(1) receptors. The present study examines if adenosine via A(1) receptors (A(1)R) interferes with pulsatile islet hormone release.

Main Methods: Pancreas was perfused in mice expressing or lacking the A(1) receptor and the hormones measured with radioimmunoassay.

Effects of external ATP on Ca(2+) signalling in endothelial cells isolated from mouse islets.

External ATP is believed to initiate and propagate Ca(2+) signals co-ordinating the insulin release pulses within and among the different islets in the pancreas. The possibility that islet endothelial cells participate in this process was evaluated by comparing the effects on [Ca(2+)](i) of purinoceptor activation in these cells with those in beta-cells. beta-Cell-rich pancreatic islets were isolated from ob/ob mice and dispersed into single cells/aggregates.

Phospholipase A2 is important for glucose induction of rhythmic Ca2+ signals in pancreatic beta cells.

Objectives: Pancreatic beta cells respond to glucose stimulation with pulses of insulin release generated by oscillatory rises of the cytoplasmic Ca2+ concentration ([Ca2+]i). The observation that exposure to external ATP and other activators of cytoplasmic phospholipase A2 (cPLA2) rapidly induces rises of [Ca2+]i similar to ordinary oscillations made it important to analyze whether suppression of the cPLA2 activity affects glucose-induced [Ca2+]i rhythmicity in pancreatic beta cells.

Methods: Ratiometric fura-2 technique was used for measuring [Ca2+]i in single beta cells and small aggregates prepared from ob/ob mouse islets.

Pulses of somatostatin release are slightly delayed compared with insulin and antisynchronous to glucagon.

It was early proposed that somatostatin-producing delta-cells in pancreatic islets have local inhibitory effects on the release of insulin and glucagon. Recent observations that pulses of insulin and glucagon are antisynchronous make it important to examine the temporal characteristics of glucose-induced somatostatin release. Analysis of 30 s fractions from the perfused rat pancreas indicated that increase of glucose from 3 to 20 mmol/l results in initial suppression of somatostatin release followed by regular 4-5 min pulses.

Glucose induces glucagon release pulses antisynchronous with insulin and sensitive to purinoceptor inhibition.

Both increase of the glucose concentration and activation of purinoceptors are known to affect pancreatic alpha-cells. Effects obtained with various purino derivatives at 2.8 and 8.

Inhibition of purinoceptors amplifies glucose-stimulated insulin release with removal of its pulsatility.

External ATP has been proposed to be an autocrine regulator of glucose-stimulated insulin secretion and responsible for the synchronization of the Ca2+ rhythmicity in the beta-cells required for a pulsatile release of insulin from the pancreas. The importance of external ATP for glucose-stimulated insulin release was evaluated in rats with the aid of 2-deoxy-N-methyladenosine-3,5-bisphosphate (MRS 2179), an inhibitor of the purinoceptors known to affect the Ca2+ signaling in beta-cells. The concentration of cytoplasmic Ca2+ was measured in single beta-cells and small aggregates with ratiometric fura-2 technique and the release of insulin recorded from isolated islets and the perfused pancreas.

External ATP triggers Ca2+ signals suited for synchronization of pancreatic beta-cells.

External ATP is supposed to trigger short-lived increases (transients) of cytoplasmic Ca2+ important for entraining insulin-secreting beta-cells into a common rhythm. To get insight into this process, rises of the cytoplasmic Ca2+ concentration ([Ca2+]i) induced by external ATP were compared with those obtained with acetylcholine, another neurotransmitter with stimulatory effects on the inositol trisphosphate (IP3) production. A ratiometric fura-2 technique was used for measuring [Ca2+]i in individual beta-cells and small aggregates isolated from ob/ob mouse islets and superfused with a medium containing methoxyverapamil.

Pulses of external ATP aid to the synchronization of pancreatic beta-cells by generating premature Ca(2+) oscillations.

Pancreatic beta-cells respond to glucose stimulation with increase of the cytoplasmic Ca(2+) concentration ([Ca(2+)](i)), manifested as membrane-derived slow oscillations sometimes superimposed with transients of intracellular origin. The effect of external ATP on the oscillatory Ca(2+) signal for pulsatile insulin release was studied by digital imaging of fura-2 loaded beta-cells and small aggregates isolated from islets of ob/ob-mice. Addition of ATP (0.

Pancreatic beta-cells communicate via intermittent release of ATP.

The role of external ATP for intercellular communication was studied in glucose-stimulated pancreatic beta-cells isolated from ob/ob mice. Digital image analyses with fura-2 revealed spontaneous transients of cytoplasmic Ca2+ appearing in synchrony in the absence of cell contacts. After removal of slow oscillations with methoxyverapamil, addition of ATP (0.

Carbon monoxide stimulates insulin release and propagates Ca2+ signals between pancreatic beta-cells.

A key question for understanding the mechanisms of pulsatile insulin release is how the underlying beta-cell oscillations of the cytoplasmic Ca2+ concentration ([Ca2+]i) are synchronized within and among the islets in the pancreas. Nitric oxide has been proposed to coordinate the activity of the beta-cells by precipitating transients of [Ca2+]i. Comparing ob/ob mice and lean controls, we have now studied the action of carbon monoxide (CO), another neurotransmitter with stimulatory effects on cGMP production.

Ligand-induced recruitment of Na+/H+-exchanger regulatory factor to the PDGF (platelet-derived growth factor) receptor regulates actin cytoskeleton reorganization by PDGF.

Proteins interacting with the human PDGF (platelet-derived growth factor) beta-receptor were isolated using immobilized peptides derived from the receptor C-terminus as a bait. We identified two PDZ domain proteins, namely NHERF (Na(+)/H(+) exchanger regulatory factor, also called EBP50) and NHERF2 (E3KARP, SIP-1, TKA-1), which have been shown previously to associate with the murine PDGF receptor [Maudsley, Zamah, Rahman, Blitzer, Luttrell, Lefkowitz and Hall (2000) Mol. Cell.

Synchronization of pancreatic beta-cell rhythmicity after glucagon induction of Ca2+ transients.

Pancreatic beta-cells are biological oscillators requiring a coupling force for the synchronization of the cytoplasmic Ca(2+) oscillations responsible for pulsatile insulin release. Testing the idea that transients, superimposed on the oscillations, are important for this synchronization, the concentration of cytoplasmic Ca(2+) ([Ca(2+)](i)) was measured with ratiometric fura-2 technique in single beta-cells and small aggregates prepared from islets isolated from ob/ob-mice. Image analyses revealed asynchronous [Ca(2+)](i) oscillations in adjacent beta-cells lacking physical contact.

Effect of transforming growth factor-beta on calcium homeostasis in prostate carcinoma cells.

Ca(2+) plays a fundamental role in the control of a variety of cellular functions, in particular, in energy metabolism and apoptosis. In this study, we show that TGF-beta at concentrations of 0.1-1.

Stretch activation of Ca2+ transients in pancreatic beta cells by mobilization of intracellular stores.

Introduction: Nonadrenergic, noncholinergic neurons have been proposed to synchronize pulsatile insulin release from the islets in the pancreas by triggering transient increases of the cytoplasmic Ca2+ concentration ([Ca2+]i) in beta-cells via an inositol trisphoshate-dependent mechanism.

Aims: To test whether pancreatic beta-cells respond to stretch activation with similar types of transients and whether these Ca signals propagate to other beta-cells in the presence and absence of cell contacts.

Methodology: Single cells and small aggregates were prepared from beta-cell-rich islets from mice.

Insulin-secreting INS-1 cells generate a novel type of poorly synchronized Ca2+ transients.

Pancreatic beta-cells have an intrinsic oscillatory Ca2+ activity supposed to be synchronized among the islets by cytoplasmic Ca2+ transients elicited by nonadrenergic, noncholinergic (NANC) neurons. To improve the understanding of this process, the cytoplasmic Ca2+ concentration ([Ca2+]i) was measured in two insulin-releasing cell lines using dual wavelength microfluorometry and the indicator fura-2. INS-1 cells but not RINm5F cells were found to generate transients of [Ca2+]i in the presence of the Ca2+ channel blocker methoxyverapamil.

Ca2+ handling of rat pancreatic beta-cells exposed to ryanodine, caffeine, and glucagon.

Reported species differences in the stimulus-secretion coupling of insulin release made it important to compare the Ca2+ handling of rat beta-cells with that previously observed in mice. Single beta-cells and small aggregates were prepared from pancreatic islets of Wistar rats, attached to cover slips and then used for measuring the cytoplasmic Ca2+ concentration ([Ca2+]i) with the ratiometric fura-2 technique. Glucose (11 mM) induced slow oscillations of [Ca2+]i similar to those seen in other species, including humans.