340-LB: Optogenetic Control of a-Cell Electrical Activity and Glucagon Secretion in Intact Islets

AbstractCharacterization of electrical activity of individual neurons is the fundamental step in understanding the functioning of the nervous system. Single cell electrical activity at various stages of cell development is essential to accurately determine in in-vivo conditions the position of a cell based on the procured electrical activity. Understanding memory formation and development translates to changes in the electrical activity of individual neurons. Hence, there is an enormous need to develop novel ways for isolating and positioning individual neurons over single recording sites. To this end, we used a 3x3 multiple microelectrode array system to spatially arrange neurons by applying a gradient AC field. We characterized the electric field distribution inside our test platform by using two dimensiona l finite element modeling (FEM) and determined the location of neurons over the electrode array. Dielectrophoretic AC fields were utilized to separate the neurons from the glial cells and to position the neurons over the electrodes. The neurons were obtained from 0-2-day-old rat (Sprague-Dawley) pups. The technique of using electric fields to achieve single neuron patterning has implications in neural engineering, elucidating a new and simpler method to develop and study neuronal activity as compared to conventional microelectrode array techniques.

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Factors Involved in the Loss of Spontaneous Contractile and Electrical Activity in Clusters of Cultured Cardiac Cells

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y72-079 ◽

1972 ◽

Vol 50 (6) ◽

pp. 523-532 ◽

Cited By ~ 7

Author(s):

O. F. Schanne

Keyword(s):

Electrical Activity ◽

Spontaneous Activity ◽

Cardiac Cells ◽

Pacemaker Activity ◽

Newborn Rats ◽

Cell Clusters ◽

A Cell ◽

Enzyme Pattern ◽

Membrane Changes ◽

Increasing Temperature

Beating cell clusters were obtained by trypsinization from hearts of newborn rats. Spontaneous activity ceased after several weeks while the cultures were still proliferating. Experiments were performed to identify the physiological determinant causing cessation of spontaneous activity. (a) Cell clusters having lost their spontaneous activity responded to extracellular stimulation. (b) Reduction of [K]o by 50% increased the number of beating cell clusters by 40%; doubling [K]o reduced the number of beating cell clusters by 49%. (c) Cell clusters which were in the process of losing their ability to contract spontaneously needed a progressively increasing temperature to induce spontaneous activity. These results suggest (1) that the pacemaker mechanism fails first when a cell cluster loses its spontaneous activity and (2) that shortly before the cluster fails to contract spontaneously, it requires more energy to maintain pacemaker activity because of possible structural membrane changes or changes in the enzyme pattern of the cells.

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Glucagon resistance and decreased susceptibility to diabetes in a model of chronic hyperglucagonemia

10.2337/figshare.13256231.v1 ◽

2020 ◽

Author(s):

Ada Admin ◽

Nadejda Bozadjieva Kramer ◽

Camila Lubaczeuski ◽

Manuel Blandino-Rosano ◽

Grant Barker ◽

...

Keyword(s):

Glucose Homeostasis ◽

Phosphoenolpyruvate Carboxykinase ◽

Cell Mass ◽

Glucagon Secretion ◽

Glucagon Receptor ◽

Glucose Levels ◽

Conditional Deletion ◽

Mtorc1 Signaling ◽

Nutrient Signaling ◽

A Cell

Elevation of glucagon levels and increase in a-cell mass are associated with states of hyperglycemia in diabetes. Our previous studies have highlighted the role of nutrient signaling via mTOR Complex 1 (mTORC1) regulation that controls glucagon secretion and a-cell mass. The current studies investigated the effects of activation of nutrient signaling by conditional deletion of the mTORC1 inhibitor, TSC2, in a-cells (aTSC2KO). We showed that activation of mTORC1 signaling is sufficient to induce chronic hyperglucagonemia as a result of a-cell proliferation, cell size and mass expansion. Hyperglucagonemia in aTSC2KO was associated with an increase in glucagon content and enhanced glucagon secretion. This model allowed us to identify the effects of chronic hyperglucagonemia on glucose homeostasis by inducing insulin secretion and resistance to glucagon in the liver. Liver glucagon resistance in aTSC2KO mice were characterized by reduced expression of the glucagon receptor (GCGR), phosphoenolpyruvate carboxykinase (PEPCK) and genes involved in amino acid metabolism and urea production. Glucagon resistance in aTSC2KO mice was associated with improved glucose levels in Streptozotocin (STZ)-induced β-cell destruction and HFD-induced glucose intolerance. These studies demonstrate that chronic hyperglucagonemia can improve glucose homeostasis by inducing glucagon resistance in the liver.

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Glucagon resistance and decreased susceptibility to diabetes in a model of chronic hyperglucagonemia

10.2337/figshare.13256231 ◽

2020 ◽

Author(s):

Nadejda Bozadjieva Kramer ◽

Camila Lubaczeuski ◽

Manuel Blandino-Rosano ◽

Grant Barker ◽

George K. Gittes ◽

...

Keyword(s):

Glucose Homeostasis ◽

Phosphoenolpyruvate Carboxykinase ◽

Cell Mass ◽

Glucagon Secretion ◽

Glucagon Receptor ◽

Glucose Levels ◽

Conditional Deletion ◽

Mtorc1 Signaling ◽

Nutrient Signaling ◽

A Cell

Elevation of glucagon levels and increase in a-cell mass are associated with states of hyperglycemia in diabetes. Our previous studies have highlighted the role of nutrient signaling via mTOR Complex 1 (mTORC1) regulation that controls glucagon secretion and a-cell mass. The current studies investigated the effects of activation of nutrient signaling by conditional deletion of the mTORC1 inhibitor, TSC2, in a-cells (aTSC2KO). We showed that activation of mTORC1 signaling is sufficient to induce chronic hyperglucagonemia as a result of a-cell proliferation, cell size and mass expansion. Hyperglucagonemia in aTSC2KO was associated with an increase in glucagon content and enhanced glucagon secretion. This model allowed us to identify the effects of chronic hyperglucagonemia on glucose homeostasis by inducing insulin secretion and resistance to glucagon in the liver. Liver glucagon resistance in aTSC2KO mice were characterized by reduced expression of the glucagon receptor (GCGR), phosphoenolpyruvate carboxykinase (PEPCK) and genes involved in amino acid metabolism and urea production. Glucagon resistance in aTSC2KO mice was associated with improved glucose levels in Streptozotocin (STZ)-induced β-cell destruction and HFD-induced glucose intolerance. These studies demonstrate that chronic hyperglucagonemia can improve glucose homeostasis by inducing glucagon resistance in the liver.

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Computational Systems Analysis of Glucose Sensitivity, Electrical Activity and Glucagon Secretion in Pancreatic Alpha-Cells

Biophysical Journal ◽

10.1016/j.bpj.2011.11.751 ◽

2012 ◽

Vol 102 (3) ◽

pp. 136a

Author(s):

Leonid Fridlyand ◽

Louis H. Philipson

Keyword(s):

Electrical Activity ◽

Systems Analysis ◽

Glucagon Secretion ◽

Alpha Cells ◽

Pancreatic Alpha Cells ◽

Glucose Sensitivity ◽

Computational Systems

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Glucagon resistance and decreased susceptibility to diabetes in a model of chronic hyperglucagonemia

10.2337/figshare.13256231.v2 ◽

2020 ◽

Author(s):

Nadejda Bozadjieva Kramer ◽

Camila Lubaczeuski ◽

Manuel Blandino-Rosano ◽

Grant Barker ◽

George K. Gittes ◽

...

Keyword(s):

Glucose Homeostasis ◽

Phosphoenolpyruvate Carboxykinase ◽

Cell Mass ◽

Glucagon Secretion ◽

Glucagon Receptor ◽

Glucose Levels ◽

Conditional Deletion ◽

Mtorc1 Signaling ◽

Nutrient Signaling ◽

A Cell

Elevation of glucagon levels and increase in a-cell mass are associated with states of hyperglycemia in diabetes. Our previous studies have highlighted the role of nutrient signaling via mTOR Complex 1 (mTORC1) regulation that controls glucagon secretion and a-cell mass. The current studies investigated the effects of activation of nutrient signaling by conditional deletion of the mTORC1 inhibitor, TSC2, in a-cells (aTSC2KO). We showed that activation of mTORC1 signaling is sufficient to induce chronic hyperglucagonemia as a result of a-cell proliferation, cell size and mass expansion. Hyperglucagonemia in aTSC2KO was associated with an increase in glucagon content and enhanced glucagon secretion. This model allowed us to identify the effects of chronic hyperglucagonemia on glucose homeostasis by inducing insulin secretion and resistance to glucagon in the liver. Liver glucagon resistance in aTSC2KO mice were characterized by reduced expression of the glucagon receptor (GCGR), phosphoenolpyruvate carboxykinase (PEPCK) and genes involved in amino acid metabolism and urea production. Glucagon resistance in aTSC2KO mice was associated with improved glucose levels in Streptozotocin (STZ)-induced β-cell destruction and HFD-induced glucose intolerance. These studies demonstrate that chronic hyperglucagonemia can improve glucose homeostasis by inducing glucagon resistance in the liver.

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Adrenaline Stimulates Glucagon Secretion in Pancreatic A-Cells by Increasing the Ca2+ Current and the Number of Granules Close to the L-Type Ca2+ Channels

The Journal of General Physiology ◽

10.1085/jgp.110.3.217 ◽

1997 ◽

Vol 110 (3) ◽

pp. 217-228 ◽

Cited By ~ 113

Author(s):

Jesper Gromada ◽

Krister Bokvist ◽

Wei-Guang Ding ◽

Sebastian Barg ◽

Karsten Buschard ◽

...

Keyword(s):

Electrical Activity ◽

Adrenergic Receptors ◽

Action Potentials ◽

Glucagon Secretion ◽

Stimulatory Action ◽

Voltage Gated ◽

A Cells ◽

Β Adrenergic Receptors ◽

Ca2 Channels ◽

Stimulation Of

We have monitored electrical activity, voltage-gated Ca2+ currents, and exocytosis in single rat glucagon-secreting pancreatic A-cells. The A-cells were electrically excitable and generated spontaneous Na+- and Ca2+-dependent action potentials. Under basal conditions, exocytosis was tightly linked to Ca2+ influx through ω-conotoxin-GVIA–sensitive (N-type) Ca2+ channels. Stimulation of the A-cells with adrenaline (via β-adrenergic receptors) or forskolin produced a greater than fourfold PKA-dependent potentiation of depolarization-evoked exocytosis. This enhancement of exocytosis was due to a 50% enhancement of Ca2+ influx through L-type Ca2+ channels, an effect that accounted for <30% of the total stimulatory action. The remaining 70% of the stimulation was attributable to an acceleration of granule mobilization resulting in a fivefold increase in the number of readily releasable granules near the L-type Ca2+ channels.

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Regulation of plasma immunoreactive glucagon in obese hyperglycaemic (ob/ob) mice

Journal of Endocrinology ◽

10.1677/joe.0.0950215 ◽

1982 ◽

Vol 95 (2) ◽

pp. 215-227 ◽

Cited By ~ 10

Author(s):

P. R. Flatt ◽

C. J. Bailey ◽

K. D. Buchanan

Keyword(s):

Cell Function ◽

Glucagon Secretion ◽

Plasma Glucagon ◽

Fasted State ◽

A Cell ◽

Old Mice ◽

Noradrenaline And Adrenaline ◽

Adrenaline Administration ◽

Suppressive Action

This study examines the role of glucagon in the pathogenesis of the obese hyperglycaemic (ob/ob) syndrome in mice. Plasma C-terminal immunoreactive glucagon concentrations were measured in fed and fasted ob/ob mice at different ages between 5–40 weeks, and in 20-week-old mice after the administration of established stimulators and inhibitors of glucagon secretion. Plasma glucagon concentrations were inappropriately raised irrespective of age, nutritional status and the accompanying prominent changes in plasma glucose and insulin concentrations. Glucose suppressed plasma glucagon in the fed but not the fasted state, suggesting a dependence on the marked hyperinsulinaemia associated with feeding. Administration of 0·25 units insulin/kg to fasted mice failed to affect plasma glucagon and glucose concentrations. Increasing the dose to 100 units/kg restored the normal suppressive actions of insulin. Fasted mice showed an exaggerated glucagon response to arginine but not to the parasympathomimetic agent pilocarpine. Fed mice displayed normal plasma glucagon responses to the sympathomimetic agents noradrenaline and adrenaline. Administration of insulin antiserum or 2-deoxy-l-glucose raised plasma glucagon concentrations of fed mice. Contrary to the lack of suppression by glucose in the fasted state, heparin-induced increase in free fatty acids reduced plasma glucagon concentrations. This study demonstrates inappropriate hyperglucagonaemia and defective A-cell function in ob/ob mice. The extent of the abnormality is exacerbated by fasting and appears to result from insensitivity of the A-cell to the normal suppressive action of insulin.

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