Selective inhibition of glucose-stimulated insulin release by dantrolene

1982 ◽  
Vol 243 (1) ◽  
pp. E59-E67 ◽  
Author(s):  
D. Janjic ◽  
C. B. Wollheim ◽  
G. W. Sharp
Keyword(s):  
Insulin Release ◽  
Selective Inhibition ◽  
Calcium Stores ◽  
Dantrolene Sodium ◽  
Voltage Dependent ◽  
14Co2 Production ◽  
Stimulus Secretion Coupling ◽  
Primary Action ◽  
Ca2 Channels

Dantrolene sodium, which interferes with excitation-contraction coupling by inhibiting the Ca2+ release from sarcoplasmic reticulum in muscle, was used to investigate the role of stored calcium in the stimulation of insulin release by various secretagogues. Insulin release was measured simultaneously with 45Ca2+ uptake or 45Ca2+ efflux from isolated rat pancreatic islets. Glucose-stimulated insulin release was inhibited by dantrolene (10–100 microM) as was glyceraldehyde- or mannose-stimulated release. In contrast, dantrolene failed to inhibit insulin release stimulated by leucine, arginine, ouabain, potassium, or 3-isobutyl-1-methylxanthine. Although dantrolene lowered glucose-stimulated 45Ca2+ uptake, nonspecific blockade of voltage-dependent Ca2+ channels may not be a primary action of dantrolene because K+-stimulated 45Ca2+ uptake was not inhibited. Glucose utilization (3H2O formation) was unaffected by dantrolene, whereas glucose oxidation (14CO2 production) was decreased. In the absence of Ca2+, the glucose-inhibited 45Ca2+ efflux was unchanged. At normal Ca2+, dantrolene inhibited glucose-stimulated 45Ca2+ efflux and veratridine induced insulin release. This suggests an interference with mobilization of beta-cell calcium stores. The selective action of dantrolene on insulin release makes it an interesting tool for further studies on stimulus-secretion coupling.

Role of intra- and extracellular calcium stores in mesothelial cell response to histamine

1995 ◽  
Vol 268 (1) ◽  
pp. L63-L70 ◽  
Author(s):  
K. Ito ◽  
M. Kuwahara ◽  
S. Sugano ◽  
M. Kuwahara
Keyword(s):  
Mesothelial Cell ◽  
Cellular Responses ◽  
Mesothelial Cells ◽  
Calcium Stores ◽  
Initial Transient ◽  
Voltage Dependent ◽  
Transient Elevation ◽  
Ca2 Channels

Ca2+ may play an important role in mesothelial cellular responses because Ca2+ acts as an intracellular messenger in a wide variety of cellular responses in different tissues. The present study was designed to clarify the mechanisms of cytosolic Ca2+ mobilization in the mesothelial cells. Rat pleural and pericardial mesothelial cells were maintained in vitro, and the Ca2+ movement was evaluated using fura 2. Histamine (30 microM to 10 mM) induced a biphasic elevation of intracellular levels of Ca2+ concentration ([Ca2+]i) that consisted of a rapid initial transient elevation followed by a sustained elevation. Neither removal of extracellular Ca2+ nor inhibition of Ca2+ influx by 1 microM nifedipine affected the histamine-induced initial transient elevation of [Ca2+]i in mesothelial cells. Nifedipine did not block histamine-induced sustained elevation of [Ca2+]i. KCl (25 and 50 mM) elicited a biphasic elevation of [Ca2+]i. However, this KCl-induced elevation of [Ca2+]i was abolished by nifedipine treatment. Ryanodine (10 microM) induced a transient elevation of [Ca2+]i in Ca(2+)-free solution. The histamine-induced elevation of [Ca2+]i was completely blocked by H1-receptor antagonists. These results suggest that the mesothelial cells have three pathways to increase [Ca2+]i: release from intracellular Ca2+ stores, Ca2+ influx through L-type voltage-dependent Ca2+ channels, and receptor-operated Ca2+ channels.

No evidence for a role of reverse Na(+)-Ca2+ exchange in insulin release from mouse pancreatic islets

1996 ◽  
Vol 271 (3) ◽  
pp. E426-E433
Author(s):  
M. J. Garcia-Barrado ◽  
P. Gilon ◽  
Y. Sato ◽  
M. Nenquin ◽  
J. C. Henquin
Keyword(s):  
Membrane Potential ◽  
B Cells ◽  
Electrical Activity ◽  
Insulin Release ◽  
Voltage Dependent ◽  
Small Rise ◽  
Mouse Pancreatic Islets ◽  
Mouse Islets ◽  
Ca2 Channels

We studied whether reverse Na(+)-Ca2+ exchange can increase cytoplasmic Ca2+ ([Ca2+]i) in mouse islets and contribute to insulin release. The exchange was stimulated by replacing Na+ with choline, sucrose, or lithium in a medium containing 15 mM glucose. Na+ omission increased electrical activity in B cells, [Ca2+]i, and insulin release. When voltage-dependent Ca2+ channels were blocked by nimodipine or closed by holding the membrane polarized with diazoxide, Na+ omission caused a slight hyperpolarization, a small rise in [Ca2+]i, and a marginal increase in insulin release (the latter only with choline). This small rise in [Ca2+]i was dependent on extracellular Ca2+ but was hardly augmented when intracellular Na+ was raised with alanine. When B cells were depolarized by 30 mM K+, Na+ omission did not affect the membrane potential but increased [Ca2+]i and insulin release. If Ca2+ channels were blocked by nimodipine, only marginal increases in Ca2+ and insulin release persisted, which were not different from those observed when the cells were not depolarized. This indicates that Ca2+ influx through voltage-dependent Ca2+ channels rather than via reverse Na(+)-Ca2+ exchange underlies the rise in [Ca2+]i and in insulin release produced by Na+ removal. No decisive support for Ca2+ influx by reverse Na(+)-Ca2+ exchange could be found.

Role of Ca2+ and Na+ on luteinizing hormone release from the calf pituitary

1988 ◽  
Vol 255 (4) ◽  
pp. E469-E474
Author(s):  
J. P. Kile ◽  
M. S. Amoss
Keyword(s):  
Luteinizing Hormone ◽  
Ionophore A23187 ◽  
Channel Blockers ◽  
Hormone Release ◽  
Primary Cells ◽  
Rat Pituitary ◽  
Voltage Dependent ◽  
Lh Release ◽  
Ca2 Channels

It has been proposed that gonadotropin-releasing hormone (GnRH) stimulates Ca2+ entry by activation of voltage-independent, receptor-mediated Ca2+ channels in the rat gonadotroph. Little work has been done on the role of calcium in GnRH-induced luteinizing hormone (LH) release in species other than the rat. Therefore, this study was done to compare the effects of agents that alter Ca2+ or Na+ entry on LH release from calf anterior pituitary primary cells in culture. GnRH (100 ng/ml), Ca2+ ionophore A23187 (2.5 microM), and the depolarizing agent ouabain (0.1-10 microM) all produced significant increases (P less than 0.05) in LH release; these effects were significantly reduced when the cells were preincubated with the organic Ca2+ channel blockers nifedipine (1-10 microM) and verapamil (1-10 microM) and with Co2+ (0.01-1 mM). The effect of ouabain was inhibited by tetrodotoxin (TTX; 1-10 nM) as well as by nifedipine at 0.1-10 microM. In contrast to its effect on rat pituitary LH release, TTX significantly inhibited GnRH-stimulated LH release at 1-100 nM. These results suggest that GnRH-induced LH release may employ Ca2+ as a second messenger in bovine gonadotrophs and support recent speculation that GnRH-induced Ca2+ mobilization may in part be voltage dependent.

Modulation of voltage-dependent Ca2+ conductance by changing Cl- concentration in rat lactotrophs

1997 ◽  
Vol 272 (4) ◽  
pp. C1178-C1185 ◽  
Author(s):  
L. Garcia ◽  
M. Fahmi ◽  
N. Prevarskaya ◽  
B. Dufy ◽  
P. Sartor
Keyword(s):  
Carboxylic Acid ◽  
Fluorescence Probe ◽  
Physiological Role ◽  
Feedback Mechanism ◽  
Pituitary Cells ◽  
Physiological Processes ◽  
Voltage Dependent ◽  
Ca2 Channels ◽  
Cl Conductance

In pituitary cells, voltage-dependent Ca2+ channels play an important role in such physiological processes as exocytosis, secretion, the cell cycle, and proliferation. Thus mechanisms that modulate voltage-dependent Ca2+ channel activity participate indirectly in regulating intracellular Ca2+ concentration. We have shown a new modulating mechanism for voltage-dependent Ca2+ channels by demonstrating that Ca2+ influx is influenced by Cl-. To evaluate the role of Cl- on Ca2+ conductance coupling, we first measured the intracellular Cl- concentration of rat lactotrophs using the Cl(-)-sensitive fluorescence probe sulfopropylquinolinium by simple microspectrofluorometry or combined with electrophysiology. We found an average intracellular Cl- concentration of rat lactotrophs of approximately 60 mM (n = 39). Using the whole cell tight-seal recording technique, we showed that a reduction in external Cl- concentration ([Cl-]o) and a decrease in Cl- conductances affected Ca2+ conductance as measured by Ba2+ movement through the Ca2+ channels (I(Ba)). Low [Cl-]o (39 mM) induced a decrease in Ca2+ entry via voltage-gated Ca2+ channels (-27.75 +/- 4% of normalized I(Ba)). Similarly, blockade of the Cl- conductance by 1 mM 9-anthracene carboxylic acid induced a decrease in I(Ba) (-26 +/- 6% of normalized I(Ba)). This modulation of I(Ba) was inhibited by 24-h pretreatment of the cells with pertussis toxin (1 microg/ml), suggesting that changes in Cl- concentration induced by low [Cl-]o and 9-anthracene carboxylic acid interfered with the phosphorylation of G proteins involved in Ca2+ channel activation. These results suggest a feedback mechanism based on constant interaction between Ca2+ and Cl-. Finally, they also emphasize the physiological role of Cl- in rat lactotrophs.

scholarly journals Effect of perchlorate on calcium uptake and insulin secretion in mouse pancreatic islets

1987 ◽  
Vol 248 (1) ◽  
pp. 109-115 ◽  
Author(s):  
J Sehlin
Keyword(s):  
Insulin Secretion ◽  
Beta Cell ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Glucose Oxidation ◽  
Calcium Uptake ◽  
Maximum Effect ◽  
Mouse Pancreatic Islets ◽  
Stimulus Secretion Coupling ◽  
Ca2 Channels

Microdissected beta-cell-rich pancreatic islets of non-inbred ob/ob mice were used in studies of how perchlorate (CIO4-) affects stimulus-secretion coupling in beta-cells. CIO4- at 16 mM potentiated D-glucose-induced insulin release, without inducing secretion at non-stimulatory glucose concentrations. The potentiation mainly applied to the first phase of stimulated insulin release. In the presence of 20 mM-glucose, the half-maximum effect of CIO4- was reached at 5.5 mM and maximum effect at 12 mM of the anion. The potentiation was reversible and inhibitable by D-mannoheptulose (20 mM) or Ca2+ deficiency. CIO4- at 1-8 mM did not affect glucose oxidation. The effects on secretion were paralleled by a potentiation of glucose-induced 45Ca2+ influx during 3 min. K+-induced insulin secretion and 45Ca2+ uptake were potentiated by 8-16 mM-CIO4-. The spontaneous inactivation of K+-induced (20.9 mM-K+) insulin release was delayed by 8 mM-CIO4-. The anion potentiated the 45Ca2+ uptake induced by glibenclamide, which is known to depolarize the beta-cell. Insulin release was not affected by 1-10 mM-trichloroacetate. It is suggested that CIO4- stimulates the beta-cell by affecting the gating of voltage-controlled Ca2+ channels.

cAMP-secretion coupling is impaired in diabetic GK/Par rat β-cells: a defect counteracted by GLP-1

2011 ◽  
Vol 301 (5) ◽  
pp. E797-E806 ◽  
Author(s):  
Manuel Dolz ◽  
Jamileh Movassat ◽  
Danielle Bailbé ◽  
Hervé Le Stunff ◽  
Marie-Hélène Giroix ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Camp Accumulation ◽  
Camp Content ◽  
Camp Generation ◽  
Stimulus Secretion Coupling ◽  
Glucagon Like Peptide 1 ◽  
The Relationship

cAMP-raising agents with glucagon-like peptide-1 (GLP-1) as the first in class, exhibit multiple actions that are beneficial for the treatment of type 2 diabetic (T2D) patients, including improvement of glucose-induced insulin secretion (GIIS). To gain additional insight into the role of cAMP in the disturbed stimulus-secretion coupling within the diabetic β-cell, we examined more thoroughly the relationship between changes in islet cAMP concentration and insulin release in the GK/Par rat model of T2D. Basal cAMP content in GK/Par islets was significantly higher, whereas their basal insulin release was not significantly different from that of Wistar (W) islets. Even in the presence of IBMX or GLP-1, their insulin release did not significantly change despite further enhanced cAMP accumulation in both cases. The high basal cAMP level most likely reflects an increased cAMP generation in GK/Par compared with W islets since 1) forskolin dose-dependently induced an exaggerated cAMP accumulation; 2) adenylyl cyclase (AC)2, AC3, and Gsα proteins were overexpressed; 3) IBMX-activated cAMP accumulation was less efficient and PDE-3B and PDE-1C mRNA were decreased. Moreover, the GK/Par insulin release apparatus appears less sensitive to cAMP, since GK/Par islets released less insulin at submaximal cAMP levels and required five times more cAMP to reach a maximal secretion rate no longer different from W. GLP-1 was able to reactivate GK/Par insulin secretion so that GIIS became indistinguishable from that of W. The exaggerated cAMP production is instrumental, since GLP-1-induced GIIS reactivation was lost in the presence the AC blocker 2′,5′-dideoxyadenosine. This GLP-1 effect takes place in the absence of any improvement of the [Ca2+]i response and correlates with activation of the cAMP-dependent PKA-dependent pathway.

The Stimulus-Secretion Coupling of Glucose-Induced Insulin Release. XLVII. The Possible Role of Calmodulin*

Endocrinology ◽  
1981 ◽  
Vol 108 (4) ◽  
pp. 1305-1312 ◽  
Author(s):  
I. VALVERDE ◽  
A. SENER ◽  
P. LEBRUN ◽  
A. HERCHUELZ ◽  
W. J. MALAISSE
Keyword(s):  
Insulin Release ◽  
Stimulus Secretion Coupling

scholarly journals Is there a role for T-type Ca2+ channels in regulation of vasomotor tone in mesenteric arterioles?This article is part of a Special Issue on Information Transfer in the Microcirculation.

2009 ◽  
Vol 87 (1) ◽  
pp. 8-20 ◽  
Author(s):  
Lars Jørn Jensen ◽  
Niels-Henrik Holstein-Rathlou
Keyword(s):  
Information Transfer ◽  
Electromechanical Coupling ◽  
Low Voltage ◽  
Vasomotor Tone ◽  
Direct Demonstration ◽  
Voltage Dependent ◽  
Small Conductance ◽  
Ca2 Channels ◽  
Peripheral Blood Pressure

The largest peripheral blood pressure drop occurs in terminal arterioles (<40 µm lumen diameter). L-type voltage-dependent Ca2+ channels (VDCCs) are considered the primary pathway for Ca2+ influx during physiologic activation of vascular smooth muscle cells (VSMC). Recent evidence suggests that T-type VDCCs are expressed in renal afferent and efferent arterioles, mesenteric arterioles, and skeletal muscle arterioles. T-type channels are small-conductance, low voltage-activated, fast-inactivating channels. Thus, their role in supplying Ca2+ for contraction of VSMC has been disputed. However, T-type channels display non-inactivating window currents, which may play a role in sustained Ca2+ entry. Here, we review the possible role of T-type channels in vasomotor tone regulation in rat mesenteric terminal arterioles. The CaV3.1 channel was immunolocalized in VSMC, whereas the CaV3.2 channel was predominantly expressed in endothelial cells. Voltage-dependent Ca2+ entry was inhibited by the new specific T-type blockers R(–)-efonidipine and NNC 55-0396. The effect of NNC 55-0396 persisted in depolarized arterioles, suggesting an unusually high activation threshold of mesenteric T-type channels. T-type channels were not necessary for conduction of vasoconstriction, but appear to be important for local electromechanical coupling in VSMC. The first direct demonstration of endothelial T-type channels warrants new investigations of their role in vascular biology.

scholarly journals Effects of trifluoperazine and pimozide on stimulus–secretion coupling in pancreatic B-cells Suggestion for a role of calmodulin?

1981 ◽  
Vol 196 (3) ◽  
pp. 771-780 ◽  
Author(s):  
Jean-Claude Henquin
Keyword(s):  
Cyclic Amp ◽  
Insulin Release ◽  
Islet Cells ◽  
Antipsychotic Agents ◽  
Secretory Process ◽  
Dependent Inhibition ◽  
Net Uptake ◽  
Stimulus Secretion Coupling ◽  
Two Phases

The possible involvement of calmodulin in insulin release was evaluated by studying the effects on intact islets of trifluoperazine and pimozide, two antipsychotic agents known to bind strongly to calmodulin in cell-free systems. Trifluoperazine (10–100μm) produced a dose- and time-dependent inhibition of the two phases of glucose-stimulated insulin release. The effect was not reversible by simple washing of the drug, but could be prevented by cytochalasin B or theophylline. Trifluoperazine also inhibited the release induced by glyceraldehyde, oxoisocaproate, tolbutamide or barium, but not that stimulated by 10mm-theophylline or 1mm-3-isobutyl-1-methylxanthine. Pimozide (0.5–10μm) also produced a dose-dependent inhibition of insulin release triggered by glucose, leucine or barium, but did not affect the release induced by methylxanthines. Glucose utilization by islet cells was not modified by trifluoperazine (25μm), which slightly increased cyclic AMP concentration in islets incubated without glucose. The drug did not prevent the increase in cyclic AMP concentration observed after 10min of glucose stimulation, but suppressed it after 60min. Basal or glucose-stimulated Ca2+ influx (5min) was unaffected by 25μm-trifluoperazine, whereas Ca2+net uptake (60min) was inhibited by 20%. Glucose-stimulated Ca2+ uptake was almost unaffected by pimozide. In a Ca2+-free medium, trifluoperazine decreased Ca2+ efflux from the islets and did not prevent the further decrease by glucose; in the presence of Ca2+, the drug again decreased Ca2+ efflux and inhibited the stimulation normally produced by glucose. In the absence of glucose, trifluoperazine lowered the rate of Rb+ efflux from the islets, decreased Rb+ influx (10min), but did not affect Rb+ net uptake (60min). It did not interfere with the ability of glucose to decrease Rb+ efflux rate further and to increase Rb+ net uptake. The results show thus that trifluoperazine does not alter the initial key events of the stimulus–secretion coupling. Its inhibition of insulin release suggests a role of calmodulin at late stages of the secretory process.

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