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E Grapengiesser

Publications and source records attributed to E Grapengiesser.

51 records · Page 3Linked to original sources
PubMed1990

The cytoplasmic Ca2+ response to glucose as an indicator of impairment of the pancreatic beta-cell function.

The effects of glucose on the cytoplasmic Ca2+ concentration (Ca2+i) regulating insulin release were investigated using pancreatic beta-cells representative for the normal and diabetic situations. Increase of the glucose concentration resulted in a slight lowering of Ca2+i followed by a rise, often manifested as high amplitude oscillations. The Ca2+i-lowering component in the glucose action associated with suppression of insulin release became particularly prominent when the beta-cells were already depolarized by tolbutamide. Glucose-induced inhibition of insulin release was observed also in experiments with rats made diabetic with streptozotocin or alloxan. Other studies indicated lowering of plasma insulin after intravenous glucose administration in patients with insulin- and noninsulin-dependent diabetes mellitus. Brief exposure of beta-cells to 2.2 mmol l-1 streptozotocin resulted in impairment of the response to glucose, manifested as disappearance of the cyclic variation of Ca2+i. The results indicate that glucose-induced depolarisation is a vulnerable process, the disturbance of which may contribute to insulin secretory defects in diabetes mellitus.

Animals↗
PubMed1990

Sulfonylurea mimics the effect of glucose in inducing large amplitude oscillations of cytoplasmic Ca2+ in pancreatic beta-cells.

The effects of the insulin-releasing sulfonylurea tolbutamide on the cytoplasmic Ca2+ concentration [( Ca2+]i) in individual pancreatic beta-cells or suspensions of beta-cells were analyzed using the probe fura-2 and dual-wavelength fluorometry. Subsequent additions of 1, 10, and 100 microM tolbutamide induced a graded response, ranging from a single [Ca2+]i peak to a sustained increase. These effects depended on the presence of extracellular Ca2+ and were reversed by the hyperglycemic sulfonamide diazoxide. The responses were diminished in the presence of albumin and varied considerably between different cells. Sometimes tolbutamide triggered slow large amplitude oscillations in [Ca2+]i similar to those induced by glucose. The increase in [Ca2+]i during each tolbutamide-induced oscillation was often more rapid than for glucose-induced oscillations. Oscillations or steady state increases in [Ca2+]i induced by glucose were little influenced by tolbutamide. However, subthreshold concentrations of glucose could reactivate [Ca2+]i response to tolbutamide that had declined. Although in several ways the abilities of glucose and tolbutamide to raise [Ca2+]i were similar, the sulfonylurea lacked a [Ca2+]i-lowering component. The latter effect of glucose was so pronounced that an increase of its concentration from 3 to 20 mM caused temporary lowering of [Ca2+]i to the basal level, even during tolbutamide stimulation. The results indicate that closure of the ATP-sensitive K(+)-channels is important for the large amplitude oscillations of [Ca2+]i the appearance of which reflects the balance between entry of Ca2+ through the voltage-dependent channels and its removal from the cytoplasm.

Animals↗
PubMed1989

Regulation of pH in individual pancreatic beta-cells as evaluated by fluorescence ratio microscopy.

Pancreatic beta-cells are known to maintain intracellular pH (pHi) at a value well above that predicted from the electrochemical gradient. The mechanisms for the active extrusion of protons were examined by continuously monitoring pHi in individual beta-cells from ob/ob mice using the fluorescent indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). In a medium nominally devoid of bicarbonate, the steady-state pHi was 6.82 +/- 0.02 and the intracellular buffering capacity was equivalent to 79 +/- 3 mM/pH unit. pHi remained unaffected after raising the glucose concentration from 3 to 20 mM, it was lowered when depolarizing the beta-cells with tolbutamide and it increased in the presence of carbachol. After removal of Na+ there was a significant drop of pHi and blockage of the pHi recovery following acid loading with the NH4+ prepulse technique. Whereas addition of amiloride had a similar, but less pronounced effect, omission of Cl- resulted in moderate alkalinisation. After switching to a medium containing bicarbonate, minor acidification was followed by adjustment of pHi to a steady state higher than the initial one. The results indicate that the acid load arising from glucose metabolism in the beta-cells is effectively buffered and the protons extruded both by Na+-H+ and Cl- -HCO3- exchangers.

Amiloride↗
PubMed1989

Free and bound sodium in pancreatic beta-cells exposed to glucose and tolbutamide.

The effects of glucose and tolbutamide on the sodium handling of the pancreatic beta-cells were evaluated by measuring the total sodium content in intact islets from ob/ob-mice by integrating flame photometry and the free ion in individual beta-cells by dual wavelength fluorometry. Whereas increasing the glucose concentration from 3 to 20 mM resulted in a lowering of sodium, the addition of 100 microM tolbutamide caused a rise. The above-mentioned effects were most marked (about 50%) for the physiologically significant free sodium. The data indicate a more important role for Na+ in the regulation of insulin release than so far acknowledged. Increase of Na+ may contribute to the secretory response to hypoglycemic sulfonylureas by providing an additional rise of cytoplasmic Ca2+.

Animals↗
PubMed1989

Three types of cytoplasmic Ca2+ oscillations in stimulated pancreatic beta-cells.

Oscillations of cytoplasmic Ca2+ (Ca2+i) involved in cell regulation have recently attracted considerable attention. In the pancreatic beta-cells an intermediate concentration of glucose (11 mM) induces large oscillations of Ca2+i with periods of 2 to 6 min. Procedures stimulating insulin secretion further, such as raising glucose to 20-30 mM or adding carbachol, ATP, theophylline, glucagon, or forskolin, often changed these oscillations into a steady increase of Ca2+i. In addition, forskolin and glucagon triggered prominent 9- to 14-s Ca2+i spikes during the intervals of increased Cai2+, whereas carbachol and ATP initiated a series of rapid spikes of decreasing magnitude and increasing duration (6-11 s). All types of oscillations depended on the presence of extracellular Ca2+i, but carbachol and ATP also induced single Cai2+ transients in the absence of the cation. The results demonstrate hitherto unknown oscillations of Ca2+i in the pancreatic beta-cell which are dependent in different ways on Ca2+ entry.

Adenosine Triphosphate↗
PubMed1989

Plasma membrane associated ATP as a regulator of the secretory activity of the pancreatic beta-cell.

beta-Cell-rich pancreatic islets from ob/ob-mice were used for evaluating how ATP associated with the plasma membrane participates in the regulation of insulin release. Increase of Ca2+ initiates insulin release from permeabilized beta-cells only in the presence of Mg-ATP. When bound to the inner part of the plasma membrane ATP depolarizes the beta-cells by closing a glucose-regulated K+-channel. It is possible that ATP in a plasma membrane compartment modulates insulin release also by stimulating ion pumps and exchange processes. ATP can regulate the secretory activity by binding also to the exterior of the beta-cells. The addition of ATP resulted in stimulation of insulin release related to polyphosphoinositide breakdown. It is suggested that the granule fusion with the plasma membrane is followed by release of sufficient amounts of ATP and ADP for activating a P2-purinoceptor. This receptor may consequently be part of a system for amplifying the secretory response to glucose and other agents facilitating the entry of Ca2+.

Adenosine Triphosphate↗
PubMed1989

Glucose effects on cytoplasmic Ca2+ of individual pancreatic beta-cells recorded by two procedures for dual-wavelength fluorometry.

Two different dual-wavelength microfluorometric systems were used to measure the cytoplasmatic Ca2+ concentration (Cai2+) of individual pancreatic beta-cells loaded with the indicator fura-2. Fluorescence was excited continuously at 340 nm with frequent manual checks at 360 nm. Alternatively, the 340/380 nm fluorescence excitation ratio was recorded based on automated samples at the two wavelengths every 10 msec. Irrespective of the experimental technique a rise of the glucose concentration from 3 to 20 mM resulted in an initial lowering of Cai2+ followed by a rise with a peak and a subsequent sustained intermediary level. The increase of Cai2+ depended on the presence of extracellular Ca2+. In some cells the pattern differed and the increase of the glucose concentration induced large oscillations of Cai2+. Glucose-induced increase of Cai2+ was associated with small rapid fluctuations, which were detectable only with the fast time-sharing approach. The characteristic Cai2+ response to glucose was maintained by some beta-cells after culture for more than 3 weeks. The results indicate that the glucose sensitivity of individual beta-cells varies, and that many electrically coupled cells within an islet collectively determine the characteristic pattern of rhythmic depolarization.

Animals↗
PubMed1989

Ca2+ oscillations in pancreatic beta-cells exposed to leucine and arginine.

Dual-wavelength microfluorometry with the fura-2 indicator was employed for continuous recordings of cytoplasmic Ca2+ (Ca2+i) in individual pancreatic beta-cells isolated from ob/ob-mice. When added to a medium containing 3 mmol l-1 glucose, both 10 mmol l-1 leucine and 20 mmol l-1 arginine induced rises in Ca2+i with periodic fluctuations. In the case of leucine, this increase was preceded by initial lowering followed by high-amplitude oscillations with a periodicity of 2-6 min. In a glucose-free medium arginine had no effect, and leucine was unable to induce more than a single peak of Ca2+i increase. When present at a concentration of 1 mmol l-1, leucine sometimes induced a couple of high-amplitude oscillations at 3 mmol l-1 glucose but lowered Ca2+i permanently in a glucose-free medium. It is likely that the high-amplitude oscillations of Ca2+i are related to the electrical activity of the beta-cells. Provided that some glucose was present, leucine initiated a similar type of Ca2+i response as obtained during glucose-induced insulin release. The observed leucine effect is therefore compatible with a role of glycolysis in generating high-amplitude Ca2+ oscillations and pulsatile insulin release.

Animals↗
PubMed1988

Glucose-induced oscillations of cytoplasmic Ca2+ in the pancreatic beta-cell.

The cytoplasmic calcium concentration (Ca2+i) was measured in individual mouse pancreatic beta-cells loaded with fura-2 by recording the 340/380 nm fluorescence excitation ratio. An increase of the glucose concentration from 3 to 20 mM, caused initial lowering of Ca2+i followed by a rise with a peak preceding constant elevation at an intermediary level. However, at 11 mM glucose there were large Ca2+i oscillations with a frequency of 1 cycle per 2-6 min. The results indicate that both first and second phase secretion depend on elevated Ca2+i, and that many electrically coupled cells collectively determine the pace of rhythmic depolarization.

Animals↗
PubMed1988

Dual effect of glucose on cytoplasmic Ca2+ in single pancreatic beta-cells.

The cytoplasmic Ca2+ concentration (Ca2+i) was measured in single pancreatic beta-cells from ob/ob-mice using the fluorescent indicator fura-2. Raising the glucose concentration from 3 to 20 mM resulted in 25% initial lowering of Ca2+i, followed by 250% rise above the basal level of 49 +/- 3 nM. Tolbutamide (100 microM) was as effective as glucose in increasing Ca2+i, although its action was more rapid and not preceded by any reduction. The results support the concept that stimulated removal of Ca2+ from the cytoplasm is an essential part of the physiological glucose effect on the pancreatic beta-cells.

Animals↗
PubMed1985

Demonstration of respiratory pigments in clonal insulin-producing beta-cells.

The amounts of cytochromes and flavoproteins in insulin-producing RINm5F-cells were investigated with dual wavelength spectroscopy. The cytochromes a, a3, b and c were present in normal stoichiometric proportions. Whereas each cytochrome occurred in a concentration corresponding to 25-75 mumol/kg protein, the total amount of flavoproteins was equivalent to about 200 mumol/kg protein. In support of the existence of a functional respiratory chain, the cytochromes reacted normally both to additions of oxygen and to the inhibitors antimycin A and amytal.

Animals↗
PubMedDate not supplied

Glucose induces temperature-dependent oscillations of cytoplasmic Ca2+ in single pancreatic beta-cells related to their electrical activity.

Glucose induces large amplitude oscillations of the cytoplasmic Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells. The effects of temperature on these oscillations were examined by monitoring [Ca2+]i continuously in single beta-cells from ob/ob-mice using dual wavelength microfluorometry. The oscillations of [Ca2+]i disappeared when the temperature was increased above 42 degrees C and were reversibly inhibited below 30 degrees C. However, cooling did not prevent a glucose response in terms of the average rise of [Ca2+]i. Since patch clamp studies of single beta-cells have indicated a random occurrence of glucose-induced action potentials at room temperature, it was important to explore how the sugar affected the electrical activity at 37 degrees C. Using the cell-attached configuration of the patch clamp technique for such analyses, the action potentials were found to occur in bursts with durations similar to the large amplitude oscillations of [Ca2+]i.

Action Potentials↗
PubMedDate not supplied

Propagation of cytoplasmic Ca2+ oscillations in clusters of pancreatic beta-cells exposed to glucose.

Digital image analysis was employed for resolving the temporal and spatial variations of the cytoplasmic Ca2+ concentration ([Ca2+]i) in pancreatic beta-cells loaded with the Ca(2+)-indicator Fura-2. Glucose-stimulated individual beta-cells exhibited large amplitude oscillations of [Ca2+]i with a mean frequency of 0.33 min-1. When Ca2+ diffusion was restricted by increasing the Ca2+ buffering capacity, the sugar-induced rise of [Ca2+]i preferentially affected the peripheral cytoplasm. When glucagon was present glucose also caused less prominent oscillations with about a 10-fold higher frequency superimposed on an elevated [Ca2+]i. In small clusters of 6-14 cells the average frequency of the large amplitude oscillations increased to 0.60 min-1. The clusters were found to contain micro-domains of electrically coupled cells with synchronized oscillations. After increasing the glucose concentration, adjacent domains became functionally coupled. The oscillations originated from different cells in the cluster. Also the fast glucagon-dependent oscillations were synchronized between cells and had different origins. The results indicate that coupling of beta-cells leads to an increased frequency of the large amplitude oscillations, and that the oscillatory characteristics are determined collectively among electrically coupled beta-cells rather than by particular pacemaker cells. In the light of these data it is necessary to reconsider the previous ideas that glucose-induced oscillations of membrane potential and [Ca2+]i require coupling between many beta-cells, and that the peak [Ca2+]i values reached during oscillations should increase with the size of the coupled cluster.

Animals↗
PubMedDate not supplied

The role of Ca2+ in the release of pancreatic islet hormones.

The role of Ca2+ in initiating exocytosis of granule-bound secretory products was evaluated with respect to pancreatic islet hormones. Apart from stimulating the transfer of the granules to the plasma membrane and their subsequent extrusion, a rise of the cytoplasmic Ca2+ concentration ([Ca2+]i) may under certain conditions also have depressive effects on insulin release. Glucose has a bidirectional action on [Ca2+]i by stimulating both the entry of the ion and its removal by organelle sequestration and outward transport. The recognition of glucose as a secretory stimulus is based on sudden transitions between oscillatory and steady-state [Ca2+]i at threshold concentrations of the sugar characteristic for the individual beta-cell. The intrinsic ability of each beta-cell to generate oscillations of [Ca2+]i and the subsequent synchronization of these signals result in a pulsatile release of insulin from isolated islets. Glucose regulation of this process is manifested as alterations of the amplitudes of the insulin pulses without effects on the frequency. It is suggested that electrical signalling from the beta-cells in combination with direct effects of glucose are important for regulating the release of glucagon and somatostatin.

Animals↗