Β-cell Activity Research Articles

The effect of ATP-sensitive K+ channels on the electrical burst activity and insulin secretion in pancreatic β-cells

In recent years, the electrical burst activity of the insulin releasing pancreatic beta-cells has attracted many experimentalists and theoreticians, largely because of its functional importance, but also because of the nonlinear nature of the burst activity. The ATP-sensitive K+ channels are believed to play an important role in electrical activity and insulin release. In this paper, we show by computer simulation how ATP and antidiabetic drugs can lengthen the plateau fraction of bursting and how these chemicals can increase the intracellular Ca2+ level in the pancreatic beta-cell.

Interleukin-1β inhibits glucokinase activity in clonal HIT-T15 β-cells

Interleukin-1β (IL-1β) has been implicated in the pathogenesis of insulin-dependent diabetes mellitus. In the present study we have investigated the effects of IL-1β on glucose metabolism in clonal HIT-T15 β cells. In the short-term (1 h), 25 U ml IL-1β significantly increased the rates of insulin release and glucose utilisation, but not glucose oxidation. In contrast, after 48 h, IL-1β inhibited insulin release and glucose utilisation and oxidation. By assaying enzymes (hexokinase, glucokinase, pyruvate dehydrogenase, glucose 6-phosphatase) and nucleotides (ATP, ADP) associated with the regulation of glycolysis and glucose oxidation, we conclude that the inhibitory effects of IL-1β may be due to impaired glucokinase activity.

Dependence of Antigen Expression on Functional State of β-Cells

Antigen expression corresponding to anti-islet cell surface monoclonal antibodies IC2 and A2B5 was studied. IC2 is a rat-rat hybridoma autoantibody produced from the BB rat; among islet cells, IC2 is beta-cell specific. A2B5 is an anti-ganglioside antibody described as labeling beta-cells. Islets of Langerhans from Lewis rats were isolated and cultured for 18 h in RPMI-1640 with five different glucose concentrations (2.2, 3.3, 5.5, 11.1, and 18.3 mM). In some experiments, islets were precultured for 2 or 3 days. After isolation of islet cells and antibody labeling, the percent of IC2+ beta-cells in the different groups increased from 33.3, 34.5, 40.9, and 57.2 to 58.6% (P less than 10(-6). For A2B5, the percent of labeled islet cells increased from 37.4, 41.8, 46.7, and 53.8 to 56.2% (P less than 10(-4). Thus, increasing glucose concentration leading to higher beta-cell activity implies an increase in antigen expression. Neither A2B5 nor IC2 reacts with insulin, as shown by absorption experiments and immune electron microscopy of binding sites. Electron microscopy of IC2-gold-labeled islet cells substantiated the beta-cell specificity of IC2. In conclusion, expression of the corresponding antigens to IC2 and A2B5 depends on the functional state of the beta-cells; because this has been shown to be an important factor in the development of insulin-dependent diabetes, our findings may be of potential pathogenetic interest.

Quinine blocks the high conductance, calcium-activated potassium channel in rat pancreatic β-cells

The [Ca 2+] i-activated K +-channel, one of the 3 K +-channels described in pancreatic β-cells, is a high conductance, voltage-dependent K +-channel. Quinine, known to block [Ca 2+] i-activated K +-channels in other cells, has been described to block the silent phase between the bursts of glucose-evoked electrical activity in mouse pancreatic β-cells, and to inhibit K + efflux from rat pancreatic islets. We report here that quinine blocks the [Ca 2+ i-activated K +-channel in rat pancreatic β-cells, from the external side of the membrane. We also show that the blockade is characterized by fast flickering of the K +-channel between the open and closed state. Mean open and closed times within bursts were found to be exponentially distributed, suggesting that the blockade by quinine involves obstruction on the K + flow through the open to be exponentially distributed, suggesting that the blockade by quinine involves obstruction on the K + flow through the open channel.

The dependence on intracellular ATP concentration of ATP-sensitive K-channels and of Na,K-ATPase in intact HIT-T15β-cells

We have studied the effects of changes of intracellular ATP concentration ([ATP] i) on the activity of ATP-sensitive K-channels ( I K(ATP)) and of Na,K-ATPase in intact cells of the insulin-secreting cell-line HIT-T15. Pre-exposure of HIT β-cells to oligomycin caused a dose-dependent reduction in [ATP] i. Marked activation of I K(ATP) activity was found when ATP was lowered below 3 mM. Na,K-ATPase was progressively inhibited as ATP was lowered to 1.5 mM. These data demonstrate that changes in intracellular ATP in the millimolar range markedly influence the activity of two β-cell membrane proteins having affinities for ATP in the micromolar range. This suggests that submembrane [ATP] may be considerably below the measured bulk cytosolic concentration. The findings also support the proposed role of intracellular ATP in mediating effects of changes in glucose concentration on the activity of β-cell I K(ATP) and insulin secretion.

Interaction of beta-cell activity and IL-1 concentration and exposure time in isolated rat islets of Langerhans.

This study was designed to test the hypothesis that target-cell activity influences the degree and time course of interleukin 1 beta (IL-1 beta)-mediated beta-cell impairment in vitro. Functional and morphological studies were performed in cultured newborn rat islets of Langerhans exposed from 6 h to 6 days to 50-2000 ng/L recombinant human IL-1 beta. Beta-Cell activity was modulated by glucose and nonglucose agents (15 mM L-leucine and 10 microM of long-acting somatostatin analogue SMS 201-995). In 11 mM glucose, 2000 ng/L of IL-1 beta caused inhibition of insulin release after approximately 6 h of exposure to IL-1 beta; in 3.3 mM glucose culture, onset of inhibition was delayed by this IL-1 beta concentration until after 48 h of exposure. Similarly, stimulation and suppression of beta-cell function with L-leucine and SMS 201-995, respectively, resulted in acceleration and delay of IL-1 beta-mediated inhibition. The dose-response curve of the IL-1 beta effect was shifted left- and rightward during high and low beta-cell activity, respectively. In analogy, increasing IL-1 beta concentration, exposure time, and beta-cell activity resulted in increasing islet disintegration. Thus, the resting beta-cell is more resistant to IL-1 beta-mediated impairment than the working beta-cell.

Single Calcium Channel Activity in Mouse Pancreatic β‐Cells

Annals of the New York Academy of SciencesVolume 560, Issue 1 p. 410-412 Single Calcium Channel Activity in Mouse Pancreatic β-Cells F. M. ASHCROFT, F. M. ASHCROFT University Laboratory of Physiology Oxford University Oxford, United KingdomSearch for more papers by this authorP. RORSMAN, P. RORSMAN Department of Medical Physics Göteborg University Göteborg, SwedenSearch for more papers by this authorG. TRUBE, G. TRUBE Max Planck Institute für Biophysikalische Chemie Göttingen, Federal Republic of GermanySearch for more papers by this author F. M. ASHCROFT, F. M. ASHCROFT University Laboratory of Physiology Oxford University Oxford, United KingdomSearch for more papers by this authorP. RORSMAN, P. RORSMAN Department of Medical Physics Göteborg University Göteborg, SwedenSearch for more papers by this authorG. TRUBE, G. TRUBE Max Planck Institute für Biophysikalische Chemie Göttingen, Federal Republic of GermanySearch for more papers by this author First published: June 1989 https://doi.org/10.1111/j.1749-6632.1989.tb24123.xCitations: 16AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume560, Issue1Calcium Channels: Structure and FunctionJune 1989Pages 410-412 RelatedInformation

Modulation of insulin secretion from beta-cells by phosphoinositide-derived second-messenger molecules.

In isolated islets, the hydrolysis of membrane phosphoinositides (PI) participates in the transduction of both extracellular and intracellular signals into an effective insulin secretory response. A wide variety of potential second-messenger molecules are generated during the phospholipase C-mediated cleavage of these strategically situated membrane phospholipids. Several distinct but interrelated issues are addressed in this perspective. These include 1) methodological approaches utilized to assess PI turnover, 2) the synergistic relationship between PI-derived second messengers and cAMP, 3) the contribution of changing PI turnover rates to the biphasic pattern of insulin output induced by 20 mM glucose, and 4) the role played by PI turnover in the phenomenon of "memory" displayed by islets after prior stimulation with various agonists. The concept that events unique to PI turnover contribute to beta-cell activation is well founded. Because of uncertainty regarding the exact nature of all PI-derived messengers, however, it is not yet possible to mold the available information into a comprehensive theory of beta-cell activation. Future studies will have to address various important unresolved issues.

Thiopental inhibits K + permeability of rat and mouse pancreatic β-cells

The effects of thiopental on the insulin release and 86Rb efflux from isolated rat islets and on parameters of the electrical activity of single β-cells of mice were studied. Thiopental 0.2 and 1.0 mM increased by 16.6 and 33.3%, respectively, the insulin release induced by 6.0 mM glucose. Thiopental reduced the 86Rb efflux rate in both 0 and 6.0 mM glucose, but had only a slight effect in 16.7 mM glucose. Menadione (20 μM) did not block the inhibitory effect of thiopental on 86Rb efflux. Thiopental induced a reversible membrane depolarization in a dose-dependent manner (0.2-1.0 mM). It also induced electrical activity at a subthreshold glucose concentration and continuous spiking in presence of 11.1 mM glucose. In the presence of 2,4-dinitrophenol (20 μM) this continuous spiking was changed to an oscillatory activity similar to that induced by 11.1 mM glucose. Thiopental (0.5 mM) induced an increase in input resistance of 12.7, 17.9 and 16.0% in 0, 5.6 and 11.1 mM glucose, respectively . The thiopental-induced changes in insulin secretion, 86Rb efflux and electrical parameters indicate that K + permeability was affected in both rat and mouse β-cells. Our results suggest that thiopental is a direct inhibitor of the glucose-sensitive K + permeability in the β-cell.

Modulation of K + conductance by intracellular pH in pancreatic β-cells

Measurements of the effects of NH 3/NH 4 + on glucose-induced electrical activity in β-cells from microdis-sected mouse islets of Langerhans and on intracellular pH in single collagenase-isolated islets pre-loaded with a fluorescent pH probe were performed and are reported here. Application of NH 3/NH + 4 (15 mM) in the presence of glucose (11 mM) promptly hyperpolarized the β-cell membrane, reduced input resistance by 60% and blocked electrical activity. These changes were paralleled by an increase in islet fluorescence indicative of a cytosolic pH increase. Removal of NH 4Cl initially stumulated electical activity, which returned to resting level with a time constant of 51 s. Concomitant with the removal of NH 4C1 there was a drop in pH i followed by a slow return to resting level with a time constant of 83 s. The results suggest that the [Ca 2+]-dependent K + channel in the β-cell membrane is activated by a rise in cytosolic pH.

Glucose-evoked changes in [K+] and [Ca2+] in the intercellular spaces of the mouse islet of Langerhans.

Microelectrode studies of the glucose-evoked burst pattern of electrical activity in pancreatic β-cells have indicated that the underlying mechanism involves the cyclic activation of K-channels.4,5,9,11,32 Furthermore, it is well documented that the action potentials during the bursts result from the activation of two voltage-gated membrane channels, Ca-channels7,8,25,31,34 and K-channels.

Fetal insulin production and complications in babies of diabetic mothers

SummaryFetal pancreatic β-cell activity was studied by measuring amniotic fluid C-peptide and insulin concentrations by radio-immunoassay in 27 pregnancies. There were 9 non-diabetics, 9 well controlled diabetics and 9 poorly controlled diabetics.There was a correlation between C-peptide and insulin concentrations in the 27 patients. There was also a correlation between C-peptide and insulin concentration and maternal blood glucose levels.The study demonstrated a clear association between fetal hyperinsulinaemia and neonatal hypoglycaemia. Similarly, fetal macrosomia was significantly related to amniotic C-peptide and insulin levels.The relationship between insulin production and surfactant maturation in the fetus and the subsequent development of neonatal respiratory distress was less straightforward. It is thought that fetal insulin production in infants of diabetic mothers may not be primarily responsible for observed differences in surfactant maturation.

Differential effects of the K + channel blockers apamin and quinine on glucose-induced electrical activity in pancreatic β-cells from a strain of ob/ob (obese) mice

The effects of apamin and quinine on glucose-induced electrical activity in pancreatic islets from ob/ob mice (Norwich colony) were compared. Apamin (40–400 nM) increased the duration of the bursts of electrical activity, whereas quinine (50–100 μM) affected only slightly the steady-state electrical response to glucose. This sensitivity to apamin and poor response to quinine contrast with the resistance to apamin and sensitivity to quinine previously reported for pancreatic islets from albino mice. The results give further support to the idea that pancreatic β-cells from ob/ob mice have a modified Ca 2+-activated K + permeability.

Glucose inhibits insulin release when not promoting the entry of calcium into the β-cells

The basal Ca 2+ permeability of islets from ob ob -mice was raised by culture in a Ca 2+-deficient medium. The resulting secretory activity upon transfer to a higher Ca 2+ concentration was significantly inhibited by 6 mM glucose although higher concentrations of the sugar further stimulated insulin release. In the presence of theophylline, the inhibitory effect of 6 mM glucose was altered into a stimulatory one. After blocking the voltage-dependent channels for Ca 2+ with D-600, 20 mM glucose did not enhance but significantly inhibited insulin release. The demonstration of a paradoxical glucose inhibition of insulin release is in accordance with recent reports that the sugar not only increases but also can lower the cytoplasmic Ca 2+ activity in the pancreatic β-cells.

Dual effects of glucose on the cytosolic Ca 2+ activity of mouse pancreatic β-cells

The cytosolic Ca 2+ activity of mouse pancreatic β-cells was studied with the intracellular fluorescent indicator quin2. When the extracellular Ca 2+ concentration was 1.20 mM, the basal cytosolic Ca 2+ activity was 162 ± 9 nM. Stimulation with 20 mM glucose increased this Ca 2+ activity by 40%. In the presence of only 0.20 mM Ca 2+ or after the addition of the voltage-dependent Ca 2+-channel blocker D-600, glucose had an opposite and more prompt effect in reducing cytosolic Ca 2+ by about 15%. It is concluded that an early result of glucose exposure is a lowering of the cytosolic Ca 2+ activity and that this effect tends to be masked by a subsequent increase of the Ca 2+ activity due to influx of Ca 2+ through the voltage-dependent Ca 2+ channels.

Normal insulin sensitivity of the islets of Langerhans in obese subjects with resistance to its glucoregulatory actions.

The ability of varying levels of circulating insulin to suppress alpha- and beta-cell secretion was assessed by plasma glucagon and C-peptide measurement in 6 obese and 6 nonobese subjects maintained in a euglycemic state, with an insulin concentration elevated by 10, 20, or 100 microU/ml above basal levels by a primed-continuous infusion of insulin. The 10-microU/ml increase did not suppress C-peptide levels significantly in either group. However, incremental increases in plasma insulin of approximately 20 and 100 microU/ml above basal suppressed plasma C-peptide by 0.27 +/- 0.14 and 0.53 +/- 0.07 pmol/ml, respectively, in the obese subjects (14% and 31% of the basal values of 2.20 +/- 0.18 and 2.19 +/- 0.26 pmol/ml, respectively) and by 0.16 +/- 0.06 and 0.17 +/- 0.06 pmol/ml in the nonobese subjects (20% and 25% the basal values of 0.74 +/- 0.11 and 0.78 +/- 0.11 pmol/ml, respectively). Plasma glucagon levels were suppressed to a similar degree in each group in a dose-related manner during both the 20-microU/ml and 100-microU/ml clamps. We were unable to identify an increment of insulin that suppressed C-peptide and/or glucagon in one group but not in another. These data demonstrate inhibition of alpha- and beta-cell secretion by insulin within its physiologic range in both non-obese and obese man, and exclude insulin resistance of alpha- and beta-cells in obese individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of the cytosolic calcium activity in clonal insulin-releasing cells exposed to glucose.

The cytosolic Ca2+ activity of insulin-releasing clonal cells (RINm5F) was studied with the intracellular fluorescent indicator quin-2. When the extracellular Ca2+ concentration was 1 mM, the basal cytosolic Ca2+ activity was 101 +/- 5 nM. Depolarization with 25 mM K+ increased this Ca2+ activity to at least 318 nM, an effect completely reversed by the voltage-dependent channel blocker D-600. In the presence of K+ alone these channels appeared to have a half-life of 6.7 +/- 0.8 min. In contrast to the action of K+, exposure of the RINm5F cells to 4 mM glucose resulted in a reduction of the cytosolic Ca2+ activity. This effect was observed during K+ depolarization but was more pronounced under basal conditions when it amounted to 20%. The data provide the first direct evidence that glucose can decrease the cytosolic Ca2+ activity in beta-cells. Unlike the case in normal beta-cells the glucose effect on the voltage-dependent Ca2+ channels in the RINm5F cells is apparently not sufficient to overcome the intracellular buffering of Ca2+. A defective depolarization is therefore a probable cause of the failing insulin secretion of RINm5F cells exposed to glucose.

Factitious Hypoglycemia

Insulin abuse resulting in hypoglycemia was originally reported in 1947.1,2 However, not until the 1970s was the serum C-peptide level recognized to be a reliable marker of pancreatic β-cell activity.3 Human C-peptide radioimmunoassay has been advocated recently as a useful test in diagnosing insulin-induced factitious hypoglycemia.4,5 This report describes a case of child abuse presenting as hypoglycemic coma secondary to insulin injection. The diagnosis was made by the presence of the pathognomonic triad: hypoglycemia, hyperinsulinemia, and low serum levels of C-peptide. CASE REPORT A 2-year-old black boy was brought to the emergency room in an unresponsive state. He was said to be unarousable after his regular afternoon nap.

The effect of staphylococcal delta-haemolysin on the secretory activity of the pancreatic beta-cell.

The secretion of insulin from isolated rat islets of Langerhans was found to be stimulated by the surface-active staphylococcal exotoxin, delta-haemolysin. The response was dependent on the concentration of delta-haemolysin, was rapid in onset, and could be maintained for at least an hour in the presence of the agent. The rate of secretion rapidly declined on removal of delta-haemolysin and the islets remained responsive to glucose following toxin treatment. Further characterization of the interaction of this agent with the beta-cell plasma membrane may provide valuable information concerning the role played by this membrane in the regulation of insulin secretion.

The electrical activity of pancreatic β-cells of diabetic mice

The electrical activity of pancreatic β-cells of diabetic mice