Regulation of insulin secretion via ATP-sensitive K+ channel independent mechanisms: role of phospholipase C

1997 ◽  
Vol 272 (4) ◽  
pp. E671-E677 ◽  
Author(s):  
W. S. Zawalich ◽  
K. C. Zawalich
Keyword(s):  
Insulin Secretion ◽  
Phospholipase C ◽  
Inositol Phosphates ◽  
Inhibitory Effect ◽  
Secretory Response ◽  
K Channel ◽  
Rat Islets ◽  
Protein Kinase C Inhibitor ◽  
Mouse Islets

Groups of rat or mouse islets were isolated and perifused with 20 mM glucose plus 200 microM diazoxide. The further addition of 30 mM K+ resulted in a rapid and sustained biphasic insulin secretory response. The onset of secretion in response to the addition of K+ was comparable in both species, but the magnitude of the response was significantly greater from rat islets. After the labeling of islet phosphoinositide pools with 2-[3H]inositol, the accumulation of labeled inositol phosphates (IP) in response to 30 mM K+ addition in the simultaneous presence of 20 mM glucose plus diazoxide was assessed. The addition of 30 mM K+ significantly increased IP accumulation approximately 300% in rat islets, whereas only an insignificant 25-30% increase was observed in mouse islets. The protein kinase C inhibitor staurosporine (50 nM) dramatically reduced the sustained secretory response from rat islets in the presence of 30 mM K+, 20 mM glucose, and diazoxide. Its effect was minimal on mouse islets and a significant inhibitory effect on insulin secretion was observed only during the final 5 min of the perifusion. The further addition of carbachol, an agonist that activates an isozyme of phospholipase C distinct from that activated by glucose, together with K+, 20 mM glucose, plus diazoxide resulted in a sustained amplification of insulin secretion from mouse but not rat islets. K+ (30 mM)-induced insulin secretion in the presence of 3 mM glucose was similar from perifused rat or mouse islets, a finding that would seem to preclude the activation of voltage-regulated Ca2+ channels as the pertinent difference. These results confirm previous observations with these species and document another anomaly that exists between the responses of rat islets compared with mouse islets. The inability to activate a nutrient- and calcium-regulated phospholipase C isozyme in mouse islets to the same extent as in rat islets appears to account, at least in part, for these different insulin secretory responses under these unique conditions.

Regulation of insulin secretion by phospholipase C

1996 ◽  
Vol 271 (3) ◽  
pp. E409-E416 ◽  
Author(s):  
W. S. Zawalich ◽  
K. C. Zawalich
Keyword(s):  
Insulin Secretion ◽  
Phospholipase C ◽  
High Glucose ◽  
Human Islets ◽  
Secretory Response ◽  
Second Phase ◽  
Release Rates ◽  
Mouse Islets ◽  
Insulin Secretory Response ◽  
Hydrolysis Of

Biphasic insulin secretion in response to a sustained glucose stimulus occurs when rat or human islets are exposed to high levels of the hexose. A transient burst of hormone secretion is followed by a rising and sustained secretory response that, in the perfused rat pancreas, is 25- to 75-fold greater than prestimulatory insulin release rates. This insulin secretory response is paralleled by a significant five- to sixfold increase in the phospholipase C (PLC)-mediated hydrolysis of islet phosphoinositide (PI) pools by high glucose. In contrast, mouse islets, when stimulated under comparable conditions with high glucose, display a second-phase response that is flat and only slightly (two- to threefold) greater than prestimulatory release rates. The minimal second-phase insulin secretory response to high glucose is accompanied by the minimal activation of PLC in mouse islets as well. However, stimulation of mouse islets with the protein kinase C (PKC) activator tetradecanoyl phorbol acetate (TPA) or the muscarinic agonist carbachol, which significantly activates an isozyme of PLC distinct from that activated by high glucose, induces a rising and sustained second-phase insulin secretory response. When previously exposed to high glucose, both rat and human islets respond to subsequent restimulation with an amplified insulin secretory response. They display priming, sensitization, or time-dependent potentiation. In contrast, mouse islets primed under similar conditions with high glucose fail to display this amplified insulin secretory response on restimulation. Mouse islets can, however, be primed by brief exposure to either TPA or carbachol. Finally, whereas rat islets are desensitized by chronic exposure to high glucose, mouse islet insulin secretory responses are relatively immune to this adverse effect of the hexose. These and other findings are discussed in relationship to the role being played by agonist-induced increases in the PLC-mediated hydrolysis of islet phosphoinositide pools and the activation of PKC in these species-specific insulin secretory response patterns.

Plasma membrane depolarization as a determinant of the first phase of insulin secretion

2009 ◽  
Vol 297 (2) ◽  
pp. E315-E322 ◽  
Author(s):  
K. Hatlapatka ◽  
M. Willenborg ◽  
I. Rustenbeck
Keyword(s):  
Plasma Membrane ◽  
Insulin Secretion ◽  
Action Potential ◽  
Membrane Depolarization ◽  
Secretory Response ◽  
Nmri Mouse ◽  
Β Cells ◽  
Mouse Islets ◽  
Kinetics Of

The role of plasma membrane depolarization as a determinant of the initial phase of insulin secretion was investigated. NMRI mouse islets and β-cells were used to measure the kinetics of insulin secretion, ATP and ADP content, membrane potential, and cytosolic free Ca2+ concentration ([Ca2+]i). The depolarization of metabolically intact β-cells by KCl corresponded closely to the theoretical values. In contrast to physiological (glucose) or pharmacological (tolbutamide) ATP-sensitive K+ (KATP) channel block, KCl depolarization did not induce action potential spiking. The depolarization by 15 mM K+ (21 mV) corresponded to the plateau depolarization by 50 or 500 μM tolbutamide; that by 40 mM K+ (41 mV) corresponded to the action potential peaks. Nifedipine and diazoxide abolished action potentials but not KCl depolarization, suggesting that the depolarizing strength of 15, but not 40 mM K+ corresponds to that of KATP channel closure. K+ (40 mM) induced a massive secretory response in the presence of 5 mM glucose, whereas 15 mM K+, like 50 μM tolbutamide, was only slightly effective, even though a marked increase in [Ca2+]i was produced. Raising glucose from 5 to 10 mM in the continued presence of 15 mM K+ resulted in a strongly enhanced biphasic response. The depolarization pattern of this combination could be mimicked by combining basal glucose with 15 mM K+ and 50 μM tolbutamide; however, the secretory response to these nonnutrients was much weaker. In conclusion, the initial secretory response to nutrient secretagogues is largely influenced by signaling mechanisms that do not involve depolarization.

scholarly journals The role of protein kinase C in cholinergic stimulation of insulin secretion from rat islets of Langerhans

1989 ◽  
Vol 264 (3) ◽  
pp. 753-758 ◽  
Author(s):  
S J Persaud ◽  
P M Jones ◽  
D Sugden ◽  
S L Howell
Keyword(s):  
Protein Kinase C ◽  
Insulin Secretion ◽  
Protein Kinase ◽  
Prolonged Exposure ◽  
Inositol Phosphates ◽  
Rat Islets ◽  
Phospholipid Hydrolysis ◽  
Kinase C ◽  
Short Term Exposure

The role of the Ca2+/phospholipid-dependent protein kinase C (PKC) in cholinergic potentiation of insulin release was investigated by measuring islet PKC activity and insulin secretion in response to carbachol (CCh), a cholinergic agonist. CCh caused a dose-dependent increase in insulin secretion from cultured rat islets at stimulatory glucose concentrations (greater than or equal to 7 mM), with maximal effects observed at 100 microM. Short-term exposure (5 min) of islets to 500 microM-CCh at 2 mM- or 20 mM-glucose resulted in redistribution of islet PKC activity from a predominantly cytosolic location to a membrane-associated form. Prolonged exposure (greater than 20 h) of islets to 200 nM-phorbol myristate acetate caused a virtual depletion of PKC activity associated with the islet cytosolic fraction. Under these conditions of PKC down-regulation, the potentiation of glucose-stimulated insulin secretion by CCh (500 microM) was significantly decreased, but not abolished. CCh stimulated the hydrolysis of inositol phospholipids in both normal and PKC-depleted islets, as assessed by the generation of radiolabelled inositol phosphates. These results suggest that the potentiation of glucose-induced insulin secretion by cholinergic agonists is partly mediated by activation of PKC as a consequence of phospholipid hydrolysis.

scholarly journals What Is the Metabolic Amplification of Insulin Secretion and Is It (Still) Relevant?

Metabolites ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 355
Author(s):  
Ingo Rustenbeck ◽  
Torben Schulze ◽  
Mai Morsi ◽  
Mohammed Alshafei ◽  
Uwe Panten
Keyword(s):  
Insulin Secretion ◽  
Beta Cell ◽  
Adenine Nucleotides ◽  
Pancreatic Beta Cell ◽  
Secretory Response ◽  
Mitochondrial Activity ◽  
Insulin Synthesis ◽  
Sequence Of Events ◽  
Insulin Granules

The pancreatic beta-cell transduces the availability of nutrients into the secretion of insulin. While this process is extensively modified by hormones and neurotransmitters, it is the availability of nutrients, above all glucose, which sets the process of insulin synthesis and secretion in motion. The central role of the mitochondria in this process was identified decades ago, but how changes in mitochondrial activity are coupled to the exocytosis of insulin granules is still incompletely understood. The identification of ATP-sensitive K+-channels provided the link between the level of adenine nucleotides and the electrical activity of the beta cell, but the depolarization-induced Ca2+-influx into the beta cells, although necessary for stimulated secretion, is not sufficient to generate the secretion pattern as produced by glucose and other nutrient secretagogues. The metabolic amplification of insulin secretion is thus the sequence of events that enables the secretory response to a nutrient secretagogue to exceed the secretory response to a purely depolarizing stimulus and is thus of prime importance. Since the cataplerotic export of mitochondrial metabolites is involved in this signaling, an orienting overview on the topic of nutrient secretagogues beyond glucose is included. Their judicious use may help to define better the nature of the signals and their mechanism of action.

scholarly journals Inhibitory Effects of Antipsychotics on Carbachol-Enhanced Insulin Secretion From Perifused Rat Islets: Role of Muscarinic Antagonism in Antipsychotic-Induced Diabetes and Hyperglycemia

Diabetes ◽  
2005 ◽  
Vol 54 (5) ◽  
pp. 1552-1558 ◽  
Author(s):  
D. E. Johnson ◽  
H. Yamazaki ◽  
K. M. Ward ◽  
A. W. Schmidt ◽  
W. S. Lebel ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Inhibitory Effects ◽  
Rat Islets

Role for GTP in glucose-induced phospholipase C activation in pancreatic islets

1996 ◽  
Vol 271 (1) ◽  
pp. E85-E95 ◽  
Author(s):  
J. Vadakekalam ◽  
M. E. Rabaglia ◽  
Q. H. Chen ◽  
S. A. Metz
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Islets ◽  
Phospholipase C ◽  
Insulin Release ◽  
Mycophenolic Acid ◽  
Phosphoinositide Hydrolysis ◽  
Intact Cells ◽  
Rat Islets ◽  
First Time ◽  
Permissive Role

We have previously demonstrated a permissive role for GTP in insulin secretion; in the current studies, we examined the effect of GTP on phospholipase C (PLC) activation to explore one possible mechanism for that observation. In rat islets preexposed to the GTP synthesis inhibitors mycophenolic acid (MPA) or mizoribine (MZ), PLC activation induced by 16.7 mM glucose (or by 20 mM alpha-ketoisocaproic acid) was inhibited 63% without altering the labeling of phosphoinositide substrates. Provision of guanine, which normalizes islet GTP content and insulin release, prevented the inhibition of PLC by MPA. Glucose-induced phosphoinositide hydrolysis was blocked by removal of extracellular Ca2+ or by diazoxide. PLC induced directly by Ca2+ influx (i.e., 40 mM K+) was reduced 42% in MPA-pretreated islets but without inhibition of the concomitant insulin release. These data indicate that glucose-induced PLC activation largely reflects Ca2+ entry and demonstrate (for the first time in intact cells) that adequate GTP is necessary for glucose (and Ca(2+)-)-induced PLC activation but not for maximal Ca(2+)-induced exocytosis.

Role of Ca2+/CaMK II in Ca(2+)-induced K+ channel inhibition in rat CCD principal cell

1995 ◽  
Vol 268 (2) ◽  
pp. F211-F219 ◽  
Author(s):  
M. Kubokawa ◽  
W. Wang ◽  
C. M. McNicholas ◽  
G. Giebisch
Keyword(s):  
Protein Kinase ◽  
Collecting Duct ◽  
Inhibitory Effect ◽  
K Channel ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Pkc Inhibitor ◽  
Control Value ◽  
Gf 109203X

The apical low-conductance K+ channel of rat cortical collecting duct (CCD) is inhibited by increased intracellular Ca2+ concentrations. This effect has been shown to be mediated at least in part by activation of protein kinase C (PKC). In the present study, we used the patch-clamp technique to examine the role of Ca2+/calmodulin-dependent protein kinase II (CaMK II) in mediating the Ca(2+)-induced inhibitory effect. In cell-attached patches of principal cells of rat tubules, clamping of intracellular Ca2+ concentration at 400 nM by using 1 microM ionomycin reduced channel activity to 26.5% of the control value. A further reduction in channel activity, to 8.8% of the control value, was observed following the addition of phorbol 12-myristate 13-acetate (PMA), an agent known to activate PKC. Pretreatment of cells with KN-62 (CaMK II inhibitor) or GF-109203X (PKC inhibitor) attenuated the inhibitory effect of Ca2+ on K+ channel activity (83.2 and 50.7% of the control value, respectively). Even in the presence of KN-62, addition of 10 microM PMA significantly decreased channel activity to 57.2% of the control value. The Ca(2+)-induced inhibition was completely abolished by simultaneous incubation with both KN-62 and GF-109203X. In inside-out patches, addition of 20 micrograms/ml CaMK II in the presence of a PKC inhibitor reduced channel activity to 66.2% of control values. It is concluded that CaMK II is involved in mediating the Ca(2+)-induced inhibition of the activity of the apical K+ channel of rat CCD.

Glucagonotropic and Glucagonostatic Effects of KATP Channel Closure and Potassium Depolarization

Endocrinology ◽  
2020 ◽  
Vol 162 (1) ◽  
Author(s):  
Eike Früh ◽  
Christin Elgert ◽  
Frank Eggert ◽  
Stephan Scherneck ◽  
Ingo Rustenbeck
Keyword(s):  
Insulin Secretion ◽  
Beta Cells ◽  
Katp Channel ◽  
Glucagon Secretion ◽  
Alpha Cells ◽  
High Potassium ◽  
Intrinsic Signal ◽  
Mouse Islets ◽  
Glucagon And Insulin

Abstract The role of depolarization in the inverse glucose-dependence of glucagon secretion was investigated by comparing the effects of KATP channel block and of high potassium. The secretion of glucagon and insulin by perifused mouse islets was simultaneously measured. Lowering glucose raised glucagon secretion before it decreased insulin secretion, suggesting an alpha cell–intrinsic signal recognition. Raising glucose affected glucagon and insulin secretion at the same time. However, depolarization by tolbutamide, gliclazide, or 15 mM KCl increased insulin secretion before the glucagon secretion receded. In contrast to the robust depolarizing effect of arginine and KCl (15 and 40 mM) on single alpha cells, tolbutamide was of variable efficacy. Only when applied before other depolarizing agents had tolbutamide a consistent depolarizing effect and regularly increased the cytosolic Ca2+ concentration. When tested on inside-out patches tolbutamide was as effective on alpha cells as on beta cells. In the presence of 1 µM clonidine, to separate insulinotropic from glucagonotropic effects, both 500 µM tolbutamide and 30 µM gliclazide increased glucagon secretion significantly, but transiently. The additional presence of 15 or 40 mM KCl in contrast led to a marked and lasting increase of the glucagon secretion. The glucagon secretion by SUR1 knockout islets was not increased by tolbutamide, whereas 40 mM KCl was of unchanged efficiency. In conclusion a strong and sustained depolarization is compatible with a marked and lasting glucagon secretion. KATP channel closure in alpha cells is less readily achieved than in beta cells, which may explain the moderate and transient glucagonotropic effect.

scholarly journals Differential effects of Ca2+-calmodulin on adenylate cyclase activity cyclase activity in mouse and rat pancreatic islets

1982 ◽  
Vol 206 (1) ◽  
pp. 97-102 ◽  
Author(s):  
P Thams ◽  
K Capito ◽  
C J Hedeskov
Keyword(s):  
Adenylate Cyclase ◽  
Pancreatic Islets ◽  
Specific Inhibitor ◽  
Particulate Fraction ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Rat Islets ◽  
Rat Pancreatic Islets ◽  
Mouse Islets

The effects of Ca2+-calmodulin on adenylate cyclase activity in EGTA-washed, 27000 g particulate fractions of mouse and rat pancreatic islets were studied. Ca2+ (10 microM)-calmodulin (1 microM) stimulated adenylate cyclase activity 53.1 +/- 5.2 (N = 6)% in the particulate fraction of rat islets. Trifluoperazine (50 microM), a specific inhibitor of calmodulin, inhibited the Ca2+-calmodulin activation of the adenylate cyclase activity of this fraction of rat islets. These results confirm previous reports dealing with Ca2+-Calmodulin and rat islet adenylate cyclase [Valverde, Vandermeers. Anjaneyulu & Malaisse (1979) Science 206, 225-227; Sharp, Wiedenkeller, Kaelin, Siegel & Wollheim (1980) Diabetes 29, 74-77]. In contrast, however, Ca2+ (1-100 microM)-calmodulin (1-10 microM) did not stimulate the adenylate cyclase activity in the EGTA-washed particulate fraction of mouse islets, and trifluoperazine (50 microM) did not inhibit the adenylate cyclase activity of this fraction of mouse islets, although some remaining calmodulin [0.18 +/- 0.05 (n = 3) microgram/mg of protein] could be demonstrated. GTP (10 microM) enhanced islet adenylate cyclase activity considerably, but did not confer any sensitivity towards Ca2+-calmodulin on mouse islet adenylate cyclase. The results question the role of calmodulin in the Ca2+-dependent rise in cyclic AMP evoked by glucose in pancreatic islets.

scholarly journals Studies on the role of inositol trisphosphate in the regulation of insulin secretion from isolated rat islets of Langerhans

1985 ◽  
Vol 228 (3) ◽  
pp. 713-718 ◽  
Author(s):  
N G Morgan ◽  
G M Rumford ◽  
W Montague
Keyword(s):  
Insulin Secretion ◽  
Islets Of Langerhans ◽  
Islet Cells ◽  
Inositol Trisphosphate ◽  
Rat Islets ◽  
Isolated Rat Islets ◽  
Rat Islets Of Langerhans ◽  
Isolated Rat ◽  
Stimulation Of

Glucose (20 mM) and carbachol (1 mM) produced a rapid increase in [3H]inositol trisphosphate (InsP3) formation in isolated rat islets of Langerhans prelabelled with myo-[3H]inositol. The magnitude of the increase in InsP3 formation was similar when either agent was used alone and was additive when they were used together. In islets prelabelled with 45Ca2+ and treated with carbachol (1 mM), the rise in InsP3 correlated with a rapid, transient, release of 45Ca2+ from the cells, consistent with mobilization of 45Ca2+ from an intracellular pool. Under these conditions, however, insulin secretion was not increased. In contrast, islets prelabelled with 45Ca2+ and exposed to 20mM-glucose exhibited a delayed and decreased 45Ca2+ efflux, but released 7-8-fold more insulin than did those exposed to carbachol. Depletion of extracellular Ca2+ failed to modify the increase in InsP3 elicited by either glucose or carbachol, whereas it selectively inhibited the efflux of 45Ca2+ induced by glucose in preloaded islets. Under these conditions, however, glucose was still able to induce a small stimulation of the first phase of insulin secretion. These results demonstrate that polyphosphoinositide metabolism, Ca2+ mobilization and insulin release can all be dissociated in islet cells, and suggest that glucose and carbachol regulate these parameters by different mechanisms.

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