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E Grapengiesser

Publications and source records attributed to E Grapengiesser.

At least 37 records · Page 2Linked to original sources
PubMed1996

Glucose induces cytoplasmic Na+ oscillations in pancreatic beta-cells.

The cytoplasmic Na+ concentration ([Na+]i) was measured in individual mouse beta-cells and islet cell aggregates using the indicator SBFI. Small oscillations of [Na+]i were occasionally observed after raising glucose from 3 to 11 mM. Distinct oscillations with a frequency of 0.29 +/- 0.02 min-1 (n = 18) and amplitudes of 7.4 +/- 0.5 mM (n = 18) were obtained when also adding the Na+ channel agonist veratridine. The oscillations were counteracted by tetrodotoxin or by lowering the glucose concentration to 3 mM. Glucose failed to induce oscillations when increasing Na+ entry by co-transport with L-glycine or raising [Na+]i by blocking the Na/K pump with ouabain. The results indicate that glucose can induce oscillations of [Na+]i in pancreatic beta-cells, although this effect is usually less obvious due to activation of an efficient Na/K pump.

Animals↗
PubMed1996

The role of plasma membrane K+ and Ca2+ permeabilities for glucose induction of slow Ca2+ oscillations in pancreatic beta-cells.

In individual pancreatic beta-cells the rise of the cytoplasmic Ca2+ concentration ([Ca2+]i), induced by 11 mM glucose, is manifested either as oscillations (0.2-0.5 min-1) or as a sustained elevation. The significance of the plasma membrane permeability of Ca2+ and K- for the establishment of these slow oscillations was investigated by dual wavelength microfluorometric measurements of [Ca2+]i in individual ob/ob mouse beta-cells loaded with fura-2. Increasing the extracellular Ca2+ to 10 mM or the addition of Ca2+ channel agonist BAY K 8644 (1 microM) or K+ channel blocker tetraethylammonium+ (TEA: 10-20 mM) caused steeper rises and higher peaks of the glucose-induced oscillations. However, when extracellular Ca2+ was lowered to 0.5 mM the oscillations were transformed into a sustained suprabasal level. When the beta-cells exhibited glucose-stimulated sustained elevation of [Ca2+]i in the presence of a physiological Ca2+ concentration (1.3 mM), it was possible to induce slow oscillations by promoting the entry of Ca2+ either by raising the extracellular Ca2+ concentration to 10 mM or adding TEA or BAY K 8644. The results indicate that glucose-induced slow oscillations of [Ca2+]i depend on the closure of ATP-regulated K+ channels and require that the rate of Ca2+ influx exceeds a critical level. Apart from an inherent periodicity in ATP production it is proposed that Ca(2+)-induced ATP consumption in the submembrane space contributes to the cyclic changes of the membrane potential determining periodic entry of Ca2+.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1995

Glucose promotes turnover of Na+ in pancreatic beta-cells.

Ouabain-induced changes of the free cytoplasmic Na+ concentration ([Na+]i) were monitored in aggregates of cells prepared from beta-cell-rich pancreatic mouse islets and the results were compared with the total islet content of sodium. The steady-state [Na+]i was lower in 20 mM glucose (11 mM) than in 3 mM glucose (14 mM). In the presence of 3 mM glucose the addition of 1 mM ouabain resulted in a rise in [Na+]i with an initial rate of 1.5 mM/min. However, the increase of total sodium corresponded to 2.8 mM/min, suggesting that rapid binding and/or sequestration of Na+ are prominent features for pancreatic beta-cells. Elevation of the glucose concentration to 20 mM increased the rate of ouabain-dependent rise of [Na+]i. The effect of glucose was mimicked by 1 mM tolbutamide or 100 microM carbachol and was counteracted by 100 nM of the alpha 2-adrenergic agonist clonidine. Glucose also accelerated the lowering of [Na+]i after withdrawal of ouabain. In promoting not only the entry but also the extrusion of Na+, glucose actually enhances the turnover of the ion in pancreatic beta-cells.

Animals↗
PubMed1995

Glucose induces oscillations of cytoplasmic Ca2+, Sr2+ and Ba2+ in pancreatic beta-cells without participation of the thapsigargin-sensitive store.

Individual pancreatic beta -cells were used to study the glucose effects on the handling of Ca2+, Sr2+ and Ba2+. In extracellular medium containing one of these ions, single beta -cells responded to 11 mM glucose with large amplitude oscillations in cytoplasmic Ca2+, Sr2+ or Ba2+ with indistinguishable average frequencies (0.30-0.33/min). The oscillations disappeared after hyperpolarization with 400 microM diazoxide. Under such hyperpolarization, glucose stimulated the sequestration of Ca2+ and Sr2+ but not of repetitively mobilized by consecutive exposures to 100 microM carbachol. A 2-3 min exposure to 100 nM of the intracellular Ca(2+)-ATPase inhibitor thapsigargin also mobilized Ca2+ and Sr2+ and irreversibly abolished subsequent release by carbachol. However, thapsigargin did not prevent the large amplitude oscillations in Ca2+, Sr2+ or Ba2+ under non-hyperpolarizing conditions although the frequency of the Ca2+ oscillations was almost doubled. The results indicate that the slow oscillatory behavior of glucose-stimulated individual beta -cells does not depend on inositol 1,4,5-trisphosphate mediated release of intracellular Ca2+.

Animals↗
PubMed1994

Synchronous oscillations of cytoplasmic Ca2+ and insulin release in glucose-stimulated pancreatic islets.

The cytoplasmic Ca2+ concentration ([Ca2+]i) was measured in single pancreatic mouse islets superfused in a system allowing concomitant recordings of insulin release. When glucose was raised from 3 to 11 mM, [Ca2+]i responded by a transient lowering followed by a rise to an average level of 192 +/- 11 nM. In 77% of the islets the rise was associated with the gradual appearance of oscillations, which were either fast (2-7/min), slow (0.3-0.9/min), or a combination of both types. The characteristics of the fast [Ca2+]i oscillations were those expected from a relationship with the electrical burst activity in islets. Accordingly, in most cases the fast oscillations were remarkably regular. The slow [Ca2+]i oscillations had characteristics similar to the large amplitude ones in individual beta-cells. Whereas glucagon and dibutyryl cAMP could transform slow islet oscillations into fast ones, the alpha 2-adrenergic agonist clonidine had the opposite effect. The rapid islet oscillations were also facilitated by elevated concentrations of extracellular Ca2+. Reinforcing the arguments for [Ca2+]i oscillations as responsible for a pulsatile insulin secretion it was possible to demonstrate that the release of the hormone from single islets is synchronized with the slow [Ca2+]i oscillations.

Animals↗
PubMed1994

Glucose-induced oscillations of Ba2+ in pancreatic beta-cells occur without involvement of intracellular mobilization.

Ba2+ was used as a substitute for Ca2+ in analyzing the mechanisms responsible for glucose-induced Ca2+ oscillations in pancreatic beta-cells. The 340/380-nm fluorescence excitation ratio was recorded in individual mouse beta-cells loaded with the indicator fura-2. In 3 mM glucose, Ba2+ entered the cell in a concentration-dependent manner and was partially extruded when the ion was removed from the medium. The extrusion of Ba2+ from the beta-cell was dependent on external Na+, suggesting that Ba2+ can substitute for Ca2+ in Na+/Ca2+ countertransport. When extracellular Ba2+ was kept between 0.3 and 0.5 mM, large amplitude oscillations (0.1-0.4 min-1) were induced by glucose at concentrations above 7 mM. The oscillations were often transformed into a sustained elevation either by increase of the glucose or Ba2+ concentrations or by the additions of glucagon, forskolin, or carbachol. Although Ba2+ could substitute for Ca2+ in the glucose-induced large amplitude oscillations, there were no Ca(2+)-like pronounced spikes superimposed on an elevated cytoplasmic Ba2+ after elevation of cyclic AMP. Neither could Ba2+ substitute for Ca2+ in being incorporated in response to glucose into a pool mobilizable by carbachol. The studies indicate that cations other than Ca2+ can oscillate in response to glucose, and that such oscillations do not require mobilization from internal pools sensitive to inositol 1,4,5-trisphosphate.

Animals↗
PubMed1994

Glucose induces oscillatory Ca2+ signalling and insulin release in human pancreatic beta cells.

Mechanisms of pulsatile insulin release in man were explored by studying the induction of oscillatory Ca2+ signals in individual beta cells and islets isolated from the human pancreas. Evidence was provided for a glucose-induced closure of ATP-regulated K+ channels, resulting in voltage-dependent entry of Ca2+. The observation of step-wise increases of capacitance in response to depolarizing pulses suggests that an enhanced influx of Ca2+ is an effective means of stimulating the secretory activity of the isolated human beta cell. Activation of muscarinic receptors (1-10 mumol/l carbachol) and of purinergic P2 receptors (0.01-1 mumol/l ATP) resulted in repetitive transients followed by sustained elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i). Periodic mobilisation of intracellular calcium was seen also when injecting 100 mumol/l GTP-gamma-S into beta cells hyperpolarized to -70 mV. Individual beta cells responded to glucose and tolbutamide with increases of [Ca2+]i, manifested either as large amplitude oscillations (frequency 0.1-0.5/min) or as a sustained elevation. Glucose regulation was based on sudden transitions between the basal and the two alternative states of raised [Ca2+]i at threshold concentrations of the sugar characteristic for the individual beta cells. The oscillatory characteristics of coupled cells were determined collectively rather than by particular pacemaker cells. In intact pancreatic islets the glucose induction of well-synchronized [Ca2+]i oscillations had its counterpart in 2-5 min pulses of insulin. Each of these pulses could be resolved into regularly occurring short insulin transients. It is concluded that glucose stimulation of insulin release in man is determined by the number of beta cells entering into a state with Ca(2+)-induced secretory pulses.

Adenosine Triphosphate↗
PubMed1994

Impaired Ca2+ response to glucose in mouse beta-cells infected with coxsackie B or Echo virus.

Five strains of Coxsackie B4 virus and one of Echo 11 virus were tested with regard to their ability to replicate in pancreatic mouse beta-cells and interfere with the alterations of the cytoplasmic Ca2+ concentration ([Ca2+]i) induced by glucose. All strains except one both multiplied and caused cytopathic effect. In a control group 68% of the beta-cells responded to 11 mM glucose with large amplitude oscillations of [Ca2+]i. After inoculation with the infectious strains these oscillations appeared in only 5% of the beta-cells, whereas the non-infectious strain did not modify the glucose effect on [Ca2+]i. Despite the virus interference with the glucose response, [Ca2+]i was increased after depolarization with excessive extracellular K+ and the oscillations were induced in most beta-cells when glucose was combined with the insulin-releasing sulfonylurea tolbutamide.

Animals↗
PubMed1993

Dual effects of Na/K pump inhibition on cytoplasmic Ca2+ oscillations in pancreatic beta-cells.

Inhibition of the Na/K pump by ouabain or removal of K+ resulted in gradual increase of intracellular sodium in beta-cell-rich pancreatic islets from ob/ob-mice exposed to 3 mM glucose. In individual beta-cells this action of ouabain was paralleled by closure of ATP-regulated K+ channels and a slow elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i). In most beta-cells an increase of the glucose concentration to 11-20 mM induced large amplitude oscillations of [Ca2+]i with a frequency of 0.2-0.5/min. Ouabain had dual actions on these glucose-induced oscillations in promoting their appearance and at higher concentrations transforming them into a sustained increase of [Ca2+]i. At 100 microM ouabain reduced the frequency of the glucose-induced oscillations but nevertheless raised the time-average [Ca2+]i by increasing the amplitudes and half-widths of the Ca2+ peaks. When high concentrations of ouabain or removal of K+ transformed the oscillations into a sustained increase of [Ca2+]i, the level reached exceeded that obtained in response to rise of glucose alone. By favoring Ca2+ entry and counteracting removal of the cation from the cytoplasm, Na/K pump inhibition perturbs the balance between the processes determining glucose-induced oscillations of [Ca2+]i.

Animals↗
PubMed1993

Cell photodamage, a potential hazard when measuring cytoplasmic Ca2+ with fura-2.

Photodamage of insulin-releasing pancreatic beta-cells during measurements of the cytoplasmic Ca2+ concentration ([Ca2+]i) with fura-2 was studied. Keeping the fluorescence intensities at low levels, regular oscillations of [Ca2+]i with a frequency of 0.2-0.5 min-1 could be recorded for more than 60 min in glucose-stimulated cells. However, after a tenfold increase of the excitation energies, oscillations disappeared in most cells, the glucose response being transformed into an elevated concentration of [Ca2+]i with irregular fluctuations. Under corresponding conditions, the loss of fluorescence due to photobleaching during the initial 10 min increased from 7 to 16% in cell-sized fura-2-containing droplets. In further attempts to investigate the effects of photodamage, cells were irradiated by pulses (< 1 ms) of intense UV light (300-400 nm). A single flash of 4-7 mJ/mm2 perturbed the oscillatory pattern with maintenance of the glucose response in terms of raised [Ca2+]i. More severe lesions obtained by repeated pulses of 13-15 mJ/mm2 involved an excessive and uncontrolled rise of [Ca2+]i. It is concluded that there is a significant potential risk of photodamage when using the fura-2 technique. In the pancreatic beta-cells, exposure to intense excitation light may even result in a selective suppression of the oscillatory response to glucose.

Animals↗
PubMed1992

Cytoplasmic Ca2+ oscillations in pancreatic beta-cells.

In the last 15 years it has been a growing interest in the cyclic variations of circulating insulin [46]. After the suggestion that this phenomenon may be due to oscillations of the beta-cell membrane potential [8,39], it was demonstrated that [Ca2+]i oscillates in the glucose-stimulated beta-cell with a similar frequency to that of pulsatile insulin release. The present review describes four types of [Ca2+]i oscillations in the pancreatic beta-cell. The slow sinusoidal oscillations, referred to as type-a, are those which most closely correspond to pulsatile insulin release. Although not affecting the properties of the type-a oscillations in individual beta-cells, the concentration of glucose is a determinant for their generation and further transformation into a sustained increase. Accordingly, cytoplasmic Ca2+ is regulated by sudden transitions between oscillatory and steady-state levels at threshold concentrations of glucose, which are characteristic for the individual beta-cell. This behaviour explains the observation of a gradual recruitment of previously non-secreting cells with increase of the extracellular glucose concentration [44]. However, it still remains to be elucidated how the sudden transitions between these three states translate into the co-ordinated slow oscillations of [Ca2+]i in the intact islet. Cyclic variations of circulating insulin require a synchronization of the [Ca2+]i cycles also among the islets in the pancreas. It is still an open question by which means the millions of islets communicate mutually to establish a pattern of pulsatile insulin release from the whole pancreas. The discovery that the beta-cell is not only the functional unit for insulin synthesis but also generates the [Ca2+]i oscillations required for pulsatile insulin release has both physiological and clinical implications. The fact that minor damage to the beta-cells prevents the type-a oscillations with maintenance of a glucose response in terms of raised [Ca2+]i reinforces previous arguments [54] that loss of insulin oscillations is an early indicator of type-2 diabetes. Further analyses of the [Ca2+]i oscillations in the beta-cells should include not only the mechanisms for their generation and subsequent propagation within or among the islets but also how modulation of their frequency affects the insulin sensitivity of various target cells. The latter approach may be important in the attempts to maintain normoglycemia under conditions minimizing the vascular effects of insulin supposed to precipitate hypertonia and atherosclerosis [70,71,77].

Animals↗
PubMed1992

Glycine transformation of Ca2+ oscillations into a sustained increase parallels potentiation of insulin release.

Increase of the glucose concentration from 3 to 11 mM resulted in a triphasic release of insulin from perifused ob/ob-mouse beta-cells. A slight inhibition was followed after 2 min by a marked peak and a less pronounced sustained response. At the lower glucose concentration glycine had only marginal effects. However, in the presence of 11 mM glucose, 1-10 mM glycine triggered an immediate and dose-dependent response with an initial peak of insulin release followed by sustained stimulation. In individual beta-cells, rise of the glucose concentration from 3 to 11 mM induced initial lowering of the cytoplasmic Ca2+ concentration ([Ca2+]i) followed by large amplitude oscillations from a level of 50-90 nM to peak values exceeding 300 nM. Already at a concentration of 1 mM, glycine transformed the oscillatory pattern into a sustained level with increase of time-average [Ca2+]i. This elevation became more pronounced in the presence of 10 mM glycine. The effects of glycine on insulin release and [Ca2+]i required extracellular Na+ and were reproduced with the N-methyl analogue sarcosine. It is suggested that glycine potentiation of secretion reflects the elevation of time-average [Ca2+]i both by increased entry and reduced elimination of the cation from the cytoplasm.

Animals↗
PubMed1992

Effects of gastrin on cytosolic free Ca2+ in individual, acid-secreting rat parietal cells.

The effects of gastrin on cytosolic free Ca2+ ([Ca2+]i) in single, isolated rat gastric parietal cells were investigated using the fluorescent probe Fura-2 and digital image analysis. [Ca2+]i was increased by gastrin (100 nM) in approximately 30% of the parietal cells, which were identified by using either the fluorescent probe acridine orange or a parietal cell-specific monoclonal antibody. In the dominant pattern observed, [Ca2+]i was elevated 50-150% and returned within 1-2 min to a value 30-60% over the basal, which was sustained until withdrawal of the stimulant or addition of the gastrin inhibitor L-365,260 (1 microM). The second, but not the first phase, was abolished in the absence of extracellular Ca2+. The results indicate the existence of functional gastrin receptors in a subpopulation of rat parietal cells.

Acids↗
PubMed1992

Glucose sensing of individual pancreatic beta-cells involves transitions between steady-state and oscillatory cytoplasmic Ca2+.

Glucose stimulation of individual pancreatic beta-cells is associated with a rise of the cytoplasmic Ca2+ concentration ([Ca2+]i) manifested either as large amplitude oscillations (0.2-0.5/min) or as a sustained increase. Determinants for the transitions between the basal and the two stimulated states have now been studied using dual-wavelength fluorometric measurements on individual ob/ob mouse beta-cells loaded with the Ca2+ indicator Fura-2. The transition from the basal state to large amplitude oscillations was induced by raising the glucose concentration to 7 mM or above. The frequencies and shapes of the [Ca2+]i cycles remained largely unaffected when raising glucose as high as 40 mM. However, in some cells the oscillatory pattern was transformed into a sustained increase of [Ca2+]i at high glucose concentrations. Although the peak values for the oscillations exceeded the steady-state increase, the time average [Ca2+]i was higher during the latter phase. Both types of glucose-induced transitions were facilitated by the presence of 1-100 nM glucagon. Protein kinase C activation by 10 nM of the phorbol ester TPA resulted in a transformation of the glucose-induced oscillations into a sustained increase of [Ca2+]i but the levels reached were considerably lower than obtained with glucose alone. It is concluded that the glucose sensing of the individual beta-cell is based on sudden transitions between steady-state and oscillating cytoplasmic Ca2+. It is these transitions rather than alterations of the oscillatory characteristics which determine the average [Ca2+]i regulating insulin release.

Animals↗
PubMed1991

Cyclic AMP as a determinant for glucose induction of fast Ca2+ oscillations in isolated pancreatic beta-cells.

The effect of glucose on the cytoplasmic Ca2+ concentration ([Ca2+]i) of pancreatic beta-cells from ob/ob-mice was examined by dual wavelength recordings of the 340/380 nm fluorescence excitation ratio of fura-2. Single beta-cells responded to 11-20 mM glucose with an initial lowering of [Ca2+]i, followed by an increase usually manifested as large amplitude oscillations (300-500 nm) with a frequency of 0.2-0.5/min (a-type). Particularly in freshly isolated beta-cells, there were also superimposed fast oscillations with frequencies of 2-8/min amplitudes in the 70-250 nM range (b-type) and sometimes pronounced [Ca2+]i transients exceeding 250 nM with durations below 10 s (c-type). After addition of 1-100 nM glucagon or 1 mM of the dibutyryl or 8-bromo derivatives of cyclic AMP, glucose generated numerous b-type oscillations superimposed on those of the a-type or on an elevated steady-state level. The duration of the b-type oscillations increased slightly when glucose was raised from 11 to 16 mM. The c-type transients probably represent a separate reaction predominantly seen when raising cyclic AMP much above its normal concentration. It is concluded that glucose can induce fast oscillations of [Ca2+]i also in isolated beta-cells, especially when measures are taken to increase their cyclic AMP content.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1991

Intracellular ATP mimics GTP-gamma-S in generating Ca2+ oscillations in pancreatic beta-cells.

Intracellular free calcium ([Ca2+]i) was measured in individual pancreatic beta-cells from mice using dual emission microfluorometry and the indicator Indo-1 applied by a patch clamp pipette. GTP-gamma-S (100 microM) injected together with 0.3 or 3 mM ATP evoked repetitive [Ca2+]i transients with a frequency of about 1 per min in beta-cells kept at a membrane potential of -70 mV. The oscillatory pattern was unaffected by the Ca2+ channel blocker verapamil (50 microM). When omitting GTP-gamma-S from the pipette medium it became evident that 3 mM ATP alone can induce oscillations. The results provide additional evidence for an important role of ATP in the ionic control of insulin release, indicating that such regulation may also involve activation of G-proteins.

Adenosine Triphosphate↗
PubMed1990

Disappearance of glucose-induced oscillations of cytoplasmic Ca2+ in pancreatic beta-cells exposed to streptozotocin or alloxan.

Dual wavelength microfluorometry and the indicator fura-2 were employed for measuring cytoplasmic Ca2+ (Ca2+i) in individual pancreatic beta-cells isolated from ob/ob-mice. In most beta-cells, a rise of external glucose from 3 to 20 mM resulted in large amplitude oscillations in Ca2+i, superimposed on a basal level of 60-90 nM. The diabetogenic agents streptozotocin and alloxan (1-4.4 mM) rapidly abolished the glucose-induced oscillations of Ca2+i. The presence of a high glucose concentration during the exposure to the drugs counteracted the action of alloxan but not that of streptozotocin. Perturbation of the cyclic variations of Ca2+i by streptozotocin did not interfere with a glucose-induced increase of the ion in mildly affected beta-cells. The most advanced lesions obtained with the exposure to the diabetogenic agents were manifested as uncontrolled and sustained increases of Ca2+i. Although disrupting the intracellular Ca2+ homeostasis by separate mechanisms, streptozotocin and alloxan may finally kill the beta-cells by activating a common suicidal process due to an excessive rise of Ca2+i.

Alloxan↗