Oscillations in cytoplasmic free calcium concentration in human pancreatic islets from subjects with normal and impaired glucose tolerance (original) (raw)
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Glucoseminduced [Ca2+]i oscillations in single human pancreatic islets
Cell Calcium, 1996
Changes in cytosolic free calcium concentration ([Ca"],) in response to stimulatory glucose concentrations were investigated in human pancreatic islets, using Fura-fluorescence imaging. Increasing glucose concentration from 3 to 11 mM caused a triphasic [Ca*+], response in human islets: an initial decrease (phase l), a rapid and transient increase (phase 2) and periodic oscillations with a frequency of 1 + 0.3 min (phase 3). Raising the glucose concentration from 11 to 16.7 mM lowered the frequency of the glucose-induced [Ca'+], oscillations to 0.15 + 0.2 min, without changes in their amplitude. Human islet [Ca'+], response to stimulatory glucose concentrations is synchronous throughout the islet. Freshly isolated human islets responded to tolbutamide (50 uM) with a rise in [Ca"+],. An increase in glucose concentration, from 3 to 16 mM, in the presence of 100 uM diazoxide, produced a decrease in [Ca'+],. It is concluded that human islets respond to glucose with regular [Ca'+], oscillations that are synchronous throughout the islet and whose duration is modulated by glucose.
Journal of Endocrinology, 2000
Oscillation of insulin release by the pancreatic islets was evaluated under stringent Ca 2+-free conditions for the first time. Isolated single rat islets were exposed to 16•7 mM glucose in the presence of 1•9 mM Ca 2+ , or under the stringent Ca 2+-free conditions (Ca 2+ omission with 1 mM EGTA, 6 µM forskolin and 100 nM phorbol 12-myristate 13-acetate). Fifteen minutes after the initiation of glucose stimulation, effluent was collected at a 6-s interval, insulin was determined in duplicate by a highly sensitive insulin radioimmunoassay, and oscillation and pulsatility of release statistically analyzed. Significant oscillation of insulin release was observed in all islets irrespective of presence and absence of Ca 2+. Significant pulsatility of release was detected in 7 of 11 islets in the presence of Ca 2+ and three of six islets in the absence of Ca 2+. In conclusion, high glucose elicits oscillatory insulin release both in the presence and absence of extracellular Ca 2+ .
Amino acid-induced [Ca,]i oscillations in single mouse pancreatic islets
The effects of amino acids on cytosolic free calcium concentration ([Ca2+]i) were measured, using fura-2 fluorescence imaging, in mouse pancreatic islets of Langerhans. 2. Slow [Ca2+]i oscillations appeared when isolated islets were incubated with a solution containing a mixture of amino acids and glucose at concentrations found in the plasma of fed animals. 3. In the presence of 11 mm glucose, alanine (5 mM) and arginine (10 mM) induced a transient rise in [Ca2+], followed by an oscillatory pattern, while leucine (3 mM) and isoleucine (10 mM) triggered the appearance of slow [Ca2+]i oscillations. 4. Also in the presence of glucose (11 mM), tolbutamide (10 ,UM) increased the duration of the glucose-induced [Ca2+]i oscillations. While tolbutamide (10 /SM) did not modify the leucineinduced slow oscillatory pattern, addition of diazoxide (10 ,ZM) resulted in the gradual appearance of [Ca2+]i oscillations which resembled the glucose-induced fast oscillations. 5. Like stimulatory glucose concentrations (11 mM), glyceraldehyde (10 mM) induced fast oscillations of [Ca2+]1. 6. Fluoroacetate (2 mM) transformed leucine-induced slow [Ca2+]i oscillations into fast [Ca2+]i oscillations. Iodoacetate (1 mM) completely inhibited any oscillatory pattern. 7. It is suggested that mitochondrially generated signals, derived from amino acid oxidative metabolism, acting in conjunction with glucose-signalled messengers, are very effective at closing ATP-dependent K+ channels (KTP). 8. We propose that metabolic regulation of KATP channels is one of the mechanisms underlying the modulation of the oscillatory [Ca2+]i response to nutrient secretagogues. Under physiological conditions pancreatic fl-cells are exposed to a mixture of nutrients (glucose, amino acids and fatty acids) together with hormonal and neural factors. Therefore, in vivo, insulin release should be the result of the combinations of the effects of all these factors on the islet cells. Changes in cytosolic free calcium concentration ([Ca2+]1) in pancreatic f8-cells play an important role in the regulation of insulin secretion (for reviews see Petersen & Findlay, 1987; Prentki & Matschinsky, 1987). The accepted model for stimulus-secretion coupling implies that the metabolism of glucose and other nutrients within the ,-cells generate signals that close KATP channels in the plasma membrane. The resulting decrease in K+ conductance causes membrane depolarization with subsequent Ca2+ influx through voltageactivated Ca2+ channels and an increase in [Ca2+]i levels (Ashcroft & Rorsman, 1991; Valdeolmillos, Nadal, Contreras & Soria, 1992). We have previously shown that intermediate glucose concentrations (7-16 mM) generate two types of [Ca2+]i oscillations. Fast [Ca2+], oscillations (frequency, 3*1 + 0-8 min-') found in the majority of the cases and slow [Ca2+]i oscillations (frequency, 0 5 + 0-2 min-') found in less than one third of the islets studied (Valdeolmillos, Santos, Contreras, Soria & Rosario, 1989). Indeed, a direct correlation between bursting electrical activity and fast [Ca2+]i oscillations has been found in whole islets of Langerhans
Diabetes, 1999
Normal mouse islets were used to determine whether oscillations of these three signals are able and necessary to trigger oscillations of insulin secretion. The approach was to minimize or abolish spontaneous oscillations and to compare the impact of forced oscillations of each signal on insulin secretion. In a control medium, repetitive increases in the glucose concentration triggered oscillations in metabolism [NAD(P)H fluorescence], [Ca 2+ ] i (fura-PE3 method), and insulin secretion. In the presence of diazoxide, metabolic oscillations persisted, but [Ca 2 + ] i and insulin oscillations were abolished. When the islets were depolarized with high K + with or without diazoxide, [ C a 2 + ] i was elevated, and insulin secretion was stimulated. Forced metabolic oscillations transiently decreased or did not affect [Ca 2 + ] i and potentiated insulin secretion with oscillations of small amplitude. These oscillations of secretion followed metabolic oscillations only when [Ca 2+ ] i did not change. When [Ca 2+ ] i fluctuated, these changes prevailed over those of metabolism for timing secretion.
Diabetes, 2006
Homeostasis of blood glucose is mainly regulated by the coordinated secretion of glucagon and insulin from ␣and -cells within the islets of Langerhans. The release of both hormones is Ca 2؉ dependent. In the current study, we used confocal microscopy and immunocytochemistry to unequivocally characterize the glucose-induced Ca 2؉ signals in ␣and -cells within intact human islets. Extracellular glucose stimulation induced an opposite response in these two cell types. Although the intracellular Ca 2؉ concentration ([Ca 2؉ ] i) in -cells remained stable at low glucose concentrations, ␣-cells exhibited an oscillatory [Ca 2؉ ] i response. Conversely, the elevation of extracellular glucose elicited an oscillatory [Ca 2؉ ] i pattern in -cells but inhibited lowglucose-induced [Ca 2؉ ] i signals in ␣-cells. These Ca 2؉ signals were synchronic among -cells grouped in clusters within the islet, although they were not coordinated among the whole -cell population. The response of ␣-cells was totally asynchronic. Therefore, both the ␣and -cell populations within human islets did not work as a syncitium in response to glucose. A deeper knowledge of ␣and -cell behavior within intact human islets is important to better understand the physiology of the human endocrine pancreas and may be useful to select high-quality islets for transplantation.
FEBS Letters, 1989
Intracellular Ca2+ levels were monitored in single, acutely isolated mouse islets of Langerhans by dual emission Indo-l fluorometry. High-frequency (3.1 min-i) [Ca*+], oscillations with a brief rising time (1-2 s) and 10 s half-width ('fast' oscillations) were detected in 11 mM glucose. Raising the glucose concentration to 16.7 mM increased the duration of these oscillations, which were otherwise absent in 5.5 mM glucose. [Caz'], waves of lower frequency (0.5 mini) and longer rising time ('slow' oscillations) were also recorded. The data indicate that "fast" oscillations are directly related to p-cell bursting electrical activity, and suggest the existence of extensive networks of electrically coupled cells in the islet.
Glucose Modulates [Ca 2+] i Oscillations in Pancreatic Islets via Ionic and Glycolytic Mechanisms
Biophysical Journal, 2006
Pancreatic islets of Langerhans display complex intracellular calcium changes in response to glucose that include fast (seconds), slow (∼5min), and mixed fast/slow oscillations; the slow and mixed oscillations are likely responsible for the pulses of plasma insulin observed in vivo. To better understand the mechanisms underlying these diverse patterns, we systematically analyzed the effects of glucose on period, amplitude, and
Diabetes, 2000
Although isolated rat islets are widely used to study in vitro insulin secretion and the underlying metabolic and ionic processes, knowledge on the properties of glucose-induced electrical activity (GIEA), a key step in glucose-response coupling, has been gathered almost exclusively from microdissected mouse islets. Using a modified intracellular recording technique, we have now compared the patterns of GIEA in collagenase-isolated rat and mouse islets. Resting membrane potentials of rat and mouse -cells were approximately-50 and-60 mV, respectively. Both rat and mouse -cells displayed prompt membrane depolarizations in response to glucose. However, whereas the latter exhibited a bursting pattern consisting of alternating hyperpolarized and depolarized active phases, rat -cells fired action potentials from a nonoscillating membrane potential at all glucose concentrations (8.4-22.0 mmol/l). This was mirrored by changes in the intracellular Ca 2+ concentration ([Ca 2+ ] i), which was oscillatory in mouse and nonoscillatory in rat islets. Stimulated rat -cells were strongly hyperpolarized by diazoxide, an activator of ATP-dependent K + channels. Glucose evoked dosedependent depolarizations and [Ca 2+ ] i increases in both rat (EC 50 5.9-6.9 mmol/l) and mouse islets (EC 50 8.3-9.5 mmol/l), although it did not affect the burst plateau potential in the latter case. We conclude that there are important differences between -cells from both species with respect to early steps in the stimulussecretion coupling cascade based on the following findings: 1) mouse -cells have a larger resting K + conductance in 2 mmol/l glucose, 2) rat -cells lack the compensatory mechanism responsible for generating membrane potential oscillations and holding the depolarized plateau potential in mouse -cells, and 3) the electrical and [Ca 2+ ] i dose-response curves in rat -cells are shifted toward lower glucose concentrations. Exploring the molecular basis of these differences may clarify several a priori assumptions on the electrophysiological properties of rat -cells, which could foster the development of new working models of pancreatic -cell function.
2016
Although isolated rat islets are widely used to study in vitro insulin secretion and the underlying metabolic and ionic processes, knowledge on the properties of glucose-induced electrical activity (GIEA), a key step in glucose-response coupling, has been gathered almost exclusively from microdissected mouse islets. Using a modified intracellular recording technique, we have now compared the patterns of GIEA in collagenase-iso-lated rat and mouse islets. Resting membrane potentials of rat and mouse -cells were approximately –50 and –60 mV, respectively. Both rat and mouse -cells displayed prompt membrane depolarizations in response to glu-cose. However, whereas the latter exhibited a bursting pattern consisting of alternating hyperpolarized and depolarized active phases, rat -cells fired action