scholarly journals Glucose Stimulates Glucagon Release in Single Rat α-Cells by Mechanisms that Mirror the Stimulus-Secretion Coupling in β-Cells

Endocrinology ◽  
2005 ◽  
Vol 146 (11) ◽  
pp. 4861-4870 ◽  
Author(s):  
Hervør Lykke Olsen ◽  
Sten Theander ◽  
Krister Bokvist ◽  
Karsten Buschard ◽  
Claes B. Wollheim ◽  
...  
Keyword(s):  
Katp Channel ◽  
Channel Blocker ◽  
Adenine Nucleotides ◽  
Glucagon Secretion ◽  
Katp Channels ◽  
Suppressive Effect ◽  
Na Channel ◽  
Glucagon Release ◽  
Stimulatory Action ◽  
Isolated Rat

In isolated rat pancreatic α-cells, glucose, arginine, and the sulfonylurea tolbutamide stimulated glucagon release. The effect of glucose was abolished by the KATP-channel opener diazoxide as well as by mannoheptulose and azide, inhibitors of glycolysis and mitochondrial metabolism. Glucose inhibited KATP-channel activity by 30% (P < 0.05; n = 5) and doubled the free cytoplasmic Ca2+ concentration. In cell-attached recordings, azide opened KATP channels. The N-type Ca2+-channel blocker ω-conotoxin and the Na+-channel blocker tetrodotoxin inhibited glucose-induced glucagon release whereas tetraethylammonium, a blocker of delayed rectifying K+ channels, increased secretion. Glucagon release increased monotonically with increasing K+ concentrations. ω-Conotoxin suppressed glucagon release to 15 mm K+, whereas a combination of ω-conotoxin and an L-type Ca2+-channel inhibitor was required to abrogate secretion in 50 mm K+. Recordings of cell capacitance revealed that glucose increased the exocytotic response evoked by membrane depolarization 3-fold. This correlated with a doubling of glucagon secretion by glucose in intact rat islets exposed to diazoxide and high K+. In whole-cell experiments, exocytosis was stimulated by reducing the cytoplasmic ADP concentration, whereas changes of the ATP concentration in the physiological range had little effect. We conclude that glucose stimulates glucagon release from isolated rat α-cells by KATP-channel closure and stimulation of Ca2+ influx through N-type Ca2+ channels. Glucose also stimulated exocytosis by an amplifying mechanism, probably involving changes in adenine nucleotides. The stimulatory action of glucose in isolated α-cells contrasts with the suppressive effect of the sugar in intact islets and highlights the primary importance of islet paracrine signaling in the regulation of glucagon release.

scholarly journals Regulation of Cloned Atp-Sensitive K Channels by Adenine Nucleotides and Sulfonylureas

2001 ◽  
Vol 118 (4) ◽  
pp. 391-406 ◽  
Author(s):  
Scott A. John ◽  
James N. Weiss ◽  
Bernard Ribalet
Keyword(s):  
Katp Channel ◽  
Adenine Nucleotides ◽  
Katp Channels ◽  
Functional Coupling ◽  
Sulfonylurea Receptor ◽  
K Channels ◽  
Channel Regulation ◽  
Channel Opening ◽  
Insight Into ◽  
Positively Charged

KATP channels, comprised of the pore-forming protein Kir6.x and the sulfonylurea receptor SURx, are regulated in an interdependent manner by adenine nucleotides, PIP2, and sulfonylureas. To gain insight into these interactions, we investigated the effects of mutating positively charged residues in Kir6.2, previously implicated in the response to PIP2, on channel regulation by adenine nucleotides and the sulfonylurea glyburide. Our data show that the Kir6.2 “PIP2-insensitive” mutants R176C and R177C are not reactivated by MgADP after ATP-induced inhibition and are also insensitive to glyburide. These results suggest that R176 and R177 are required for functional coupling to SUR1, which confers MgADP and sulfonylurea sensitivity to the KATP channel. In contrast, the R301C and R314C mutants, which are also “PIP2-insensitive,” remained sensitive to stimulation by MgADP in the absence of ATP and were inhibited by glyburide. Based on these findings, as well as previous data, we propose a model of the KATP channel whereby in the presence of ATP, the R176 and R177 residues on Kir6.2 form a specific site that interacts with NBF1 bound to ATP on SUR1, promoting channel opening by counteracting the inhibition by ATP. This interaction is facilitated by binding of MgADP to NBF2 and blocked by binding of sulfonylureas to SUR1. In the absence of ATP, since KATP channels are not blocked by ATP, they do not require the counteracting effect of NBF1 interacting with R176 and R177 to open. Nevertheless, channels in this state remain activated by MgADP. This effect may be explained by a direct stimulatory interaction of NBF2/MgADP moiety with another region of Kir6.2 (perhaps the NH2 terminus), or by NBF2/MgADP still promoting a weak interaction between NBF1 and Kir6.2 in the absence of ATP. The region delimited by R301 and R314 is not involved in the interaction with NBF1 or NBF2, but confers additional PIP2 sensitivity.

scholarly journals The Cardiovascular Effects of Central Hydrogen Sulfide Are Related to KATP Channels Activation

2011 ◽  
pp. 729-738 ◽  
Author(s):  
W.-Q. LIU ◽  
C. CHAI ◽  
X.-Y. LI ◽  
W.-J. YUAN ◽  
W.-Z. WANG ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Hydrogen Sulfide ◽  
Katp Channel ◽  
Channel Blocker ◽  
Cardiovascular Effects ◽  
Katp Channels ◽  
Channel Activation ◽  
The Central Nervous System ◽  
Dose Dependent Decrease ◽  
Dose Dependent

Hydrogen sulfide (H2S), an endogenous “gasotransmitter”, exists in the central nervous system. However, the central cardiovascular effects of endogenous H2S are not fully determined. The present study was designed to investigate the central cardiovascular effects and its possible mechanism in anesthetized rats. Intracerebroventricular (icv) injection of NaHS (0.17~17 μg) produced a significant and dose-dependent decrease in blood pressure (BP) and heart rate (HR) (P<0.05) compared to control. The higher dose of NaHS (17 μg, n=6) decreased BP and HR quickly of rats and 2 of them died of respiratory paralyse. Icv injection of the cystathionine beta-synthetase (CBS) activator s-adenosyl-L-methionine (SAM, 26 μg) also produced a significant hypotension and bradycardia, which were similar to the results of icv injection of NaHS. Furthermore, the hypotension and bradycardia induced by icv NaHS were effectively attenuated by pretreatment with the KATP channel blocker glibenclamide but not with the CBS inhibitor hydroxylamine. The present study suggests that icv injection of NaHS produces hypotension and bradycardia, which is dependent on the KATP channel activation.

Effects of gastric inhibitory polypeptide (GIP) and related analogues on glucagon release at normo- and hyperglycaemia in Wistar rats and isolated islets

2008 ◽  
Vol 389 (2) ◽  
pp. 189-193 ◽  
Author(s):  
Roslyn S. Cassidy ◽  
Nigel Irwin ◽  
Peter R. Flatt
Keyword(s):  
Wistar Rats ◽  
Therapeutic Potential ◽  
Intraperitoneal Administration ◽  
Glucagon Secretion ◽  
Glucagon Release ◽  
Concurrent Administration ◽  
Rat Islets ◽  
Isolated Rat Islets ◽  
Isolated Rat

Abstract Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone secreted by endocrine K-cells in response to nutrient absorption. This study has utilised numerous well-characterised dipeptidyl peptidase IV-resistant GIP analogues to evaluate the glucagonotropic actions of GIP in Wistar rats and isolated rat islets. Intraperitoneal administration of GIP analogues (25 nmol/kg body weight) in combination with glucose had no effect on circulating glucagon concentrations compared to controls in Wistar rats. However, plasma glucose concentrations were significantly (p<0.05 to p<0.001) lowered by the GIP-receptor agonists, N-AcGIP, GIP(Lys37)PAL and N-AcGIP(Lys37)PAL. The GIP antagonist, (Pro3)GIP, caused a significant (p<0.05) reduction in glucagon levels following concurrent administration with saline in Wistar rats. In isolated rat islets native GIP induced a significant (p<0.01) enhancement of glucagon release at basal glucose concentrations, which was completely annulled by (Pro3)GIP. Furthermore, glucagon release in the presence of GLP-1, GIP(Lys37)PAL, N-AcGIP(Lys37)PAL and (Pro3)GIP was significantly (p<0.05 to p<0.001) decreased compared to native GIP in isolated rat islets. These data indicate a modest effect of GIP on glucagon secretion from isolated rat islets, which was not observed in vivo. However, the GIP agonists N-AcGIP, GIP(Lys37)PAL and N-AcGIP(Lys37)PAL had no effect on glucagon release demonstrating an improved therapeutic potential for the treatment of type 2 diabetes.

Role of potassium channels in hypoxic relaxation of porcine bronchi in vitro

1994 ◽  
Vol 266 (3) ◽  
pp. L232-L237
Author(s):  
K. S. Lindeman ◽  
L. B. Fernandes ◽  
T. L. Croxton ◽  
C. A. Hirshman
Keyword(s):  
Smooth Muscle ◽  
Dose Response ◽  
Katp Channel ◽  
Response Curve ◽  
Channel Blocker ◽  
Katp Channels ◽  
Response Curves ◽  
Third Order

To elucidate the mechanism of hypoxic relaxation of airway smooth muscle in vitro, we investigated the role of adenosine triphosphate-sensitive potassium (KATP) channels in this response. Second- and third-order porcine bronchial rings were suspended in 10-ml organ baths containing Krebs-Henseleit solution. To demonstrate the presence of KATP channels in this tissue, bronchial rings were contracted with carbachol (1 microM) in the presence of glibenclamide (100 microM), a KATP channel blocker, or the vehicle dimethyl sulfoxide (DMSO) (0.1 ml), and dose-response curves to levcromakalim (a KATP channel opener) or isoproterenol were constructed. In separate experiments, either glibenclamide or DMSO was added to the chamber and rings were contracted with carbachol (1 microM) in the presence of 95% O2-5% CO2. At the plateau, airways were relaxed with either isoproterenol (0.1 or 0.3 microM) or hypoxia (50, 28, or 0% O2, with constant 5% CO2). Glibenclamide, when compared with DMSO, shifted the dose-response curve to levcromakalim, but not to isoproterenol. Glibenclamide attenuated hypoxic relaxation in rings exposed to 50% O2 (from 35 +/- 4% to 23 +/- 3%, n = 6, P < 0.001) and increased the time to 63% relaxation in rings exposed to 50% O2 or to 28% O2. Responses in rings exposed to 0% O2 or to isoproterenol (0.1 or 0.3 microM) were not significantly altered. The ability of glibenclamide to attenuate the maximum response to 50% O2 and to increase the time to 63% relaxation during exposure to 50 or 28% O2 suggests that one component of hypoxic bronchodilation during moderate degrees of hypoxia is opening of KATP channels.

Different responses of epicardium and endocardium to KATP channel modulators during regional ischemia

1996 ◽  
Vol 271 (1) ◽  
pp. H140-H147 ◽  
Author(s):  
S. Miyoshi ◽  
T. Miyazaki ◽  
K. Moritani ◽  
S. Ogawa
Keyword(s):  
Action Potentials ◽  
Katp Channel ◽  
Channel Blocker ◽  
Katp Channels ◽  
The Third ◽  
Regional Ischemia ◽  
Monophasic Action Potentials ◽  
Anesthetized Dogs ◽  
The Difference ◽  
Shortening Rate

We examined the responses of epicardial (Epi) and endocardial (Endo) layers to ATP-sensitive K+ (KATP) channel modulators during regional ischemia in anesthetized dogs. Five-minute occlusion of the left anterior descending coronary artery was repeated at 30-min interval. Monophasic action potentials (MAPs) and extracellular K+ concentrations ([K+]o) were measured at Epi and Endo layers. 5-Hydroxydecanoate (5-HD, 30 mg/kg iv), a KATP channel blocker, or nicorandil (NCR, 0.2-0.5 mg/kg iv), an opener, was administered before the third or fourth occlusion. Shortening rate of action potential duration at 90% repolarization (APD90) was greater at the Epi layer than at the Endo layer during the first 4 min after the second control occlusion (19.7 +/- 1.5 vs. 13.1 +/- 2.4%, n = 14, P < 0.05). 5-HD suppressed the shortening preferentially at the Epi layer and reduced the difference between the two layers (11.0 +/- 3.5 vs. 11.5 +/- 3.7%, n = 6, NS). In contrast, NCR augmented the shortening preferentially at the Epi layer and increased the difference between the two layers at 4 min (29.0 +/- 2.0 vs. 5.9 +/- 3.0%, n = 6, P < 0.05). The time differentiation of [K+]o rise was similar at the two layers during the control occlusion (0.44 vs. 0.50 mM/min, n = 12). 5-HD reduced the rate of [K+]o rise at both layers (0.34 vs. 0.40 mM/min), whereas NCR augmented the rate at the Epi layer (0.82 vs. 0.50 mM/min). Activation of KATP channels appears to be involved in ischemia-induced APD shortening and [K+]o rise. The different responses of the two layers suggest a lower threshold for activation and/or a denser distribution of KATP channels or other K+ channels at the Epi layer.

scholarly journals Sulfonylureas suppress the stimulatory action of Mg-nucleotides on Kir6.2/SUR1 but not Kir6.2/SUR2A KATP channels: A mechanistic study

2014 ◽  
Vol 144 (5) ◽  
pp. 469-486 ◽  
Author(s):  
Peter Proks ◽  
Heidi de Wet ◽  
Frances M. Ashcroft
Keyword(s):  
Katp Channel ◽  
Neonatal Diabetes ◽  
Katp Channels ◽  
Nucleotide Binding ◽  
Mechanistic Study ◽  
Xenopus Laevis Oocytes ◽  
Sulfonylurea Receptor ◽  
Β Cell ◽  
Stimulatory Action ◽  
Channel Inhibition

Sulfonylureas, which stimulate insulin secretion from pancreatic β-cells, are widely used to treat both type 2 diabetes and neonatal diabetes. These drugs mediate their effects by binding to the sulfonylurea receptor subunit (SUR) of the ATP-sensitive K+ (KATP) channel and inducing channel closure. The mechanism of channel inhibition is unusually complex. First, sulfonylureas act as partial antagonists of channel activity, and second, their effect is modulated by MgADP. We analyzed the molecular basis of the interactions between the sulfonylurea gliclazide and Mg-nucleotides on β-cell and cardiac types of KATP channel (Kir6.2/SUR1 and Kir6.2/SUR2A, respectively) heterologously expressed in Xenopus laevis oocytes. The SUR2A-Y1206S mutation was used to confer gliclazide sensitivity on SUR2A. We found that both MgATP and MgADP increased gliclazide inhibition of Kir6.2/SUR1 channels and reduced inhibition of Kir6.2/SUR2A-Y1206S. The latter effect can be attributed to stabilization of the cardiac channel open state by Mg-nucleotides. Using a Kir6.2 mutation that renders the KATP channel insensitive to nucleotide inhibition (Kir6.2-G334D), we showed that gliclazide abolishes the stimulatory effects of MgADP and MgATP on β-cell KATP channels. Detailed analysis suggests that the drug both reduces nucleotide binding to SUR1 and impairs the efficacy with which nucleotide binding is translated into pore opening. Mutation of one (or both) of the Walker A lysines in the catalytic site of the nucleotide-binding domains of SUR1 may have a similar effect to gliclazide on MgADP binding and transduction, but it does not appear to impair MgATP binding. Our results have implications for the therapeutic use of sulfonylureas.

scholarly journals γ-Hydroxybutyrate does not mediate glucose inhibition of glucagon secretion

2020 ◽  
Vol 295 (16) ◽  
pp. 5419-5426
Author(s):  
Qian Yu ◽  
Bao Khanh Lai ◽  
Parvin Ahooghalandari ◽  
Anders Helander ◽  
Erik Gylfe ◽  
...  
Keyword(s):  
Glucagon Secretion ◽  
Suppressive Effect ◽  
Inhibitory Effect ◽  
Human Islets ◽  
Glucagon Release ◽  
Paracrine Factors ◽  
Glucose Inhibition ◽  
Mouse Islets ◽  
Blood Glucose Concentrations ◽  
Effect Of Glucose

Hypersecretion of glucagon from pancreatic α-cells strongly contributes to diabetic hyperglycemia. Moreover, failure of α-cells to increase glucagon secretion in response to falling blood glucose concentrations compromises the defense against hypoglycemia, a common complication in diabetes therapy. However, the mechanisms underlying glucose regulation of glucagon secretion are poorly understood and likely involve both α-cell–intrinsic and intraislet paracrine signaling. Among paracrine factors, glucose-stimulated release of the GABA metabolite γ-hydroxybutyric acid (GHB) from pancreatic β-cells might mediate glucose suppression of glucagon release via GHB receptors on α-cells. However, the direct effects of GHB on α-cell signaling and glucagon release have not been investigated. Here, we found that GHB (4–10 μm) lacked effects on the cytoplasmic concentrations of the secretion-regulating messengers Ca2+ and cAMP in mouse α-cells. Glucagon secretion from perifused mouse islets was also unaffected by GHB at both 1 and 7 mm glucose. The GHB receptor agonist 3-chloropropanoic acid and the antagonist NCS-382 had no effects on glucagon secretion and did not affect stimulation of secretion induced by a drop in glucose from 7 to 1 mm. Inhibition of endogenous GHB formation with the GABA transaminase inhibitor vigabatrin also failed to influence glucagon secretion at 1 mm glucose and did not prevent the suppressive effect of 7 mm glucose. In human islets, GHB tended to stimulate glucagon secretion at 1 mm glucose, an effect mimicked by 3-chloropropanoic acid. We conclude that GHB does not mediate the inhibitory effect of glucose on glucagon secretion.

scholarly journals Insulin Regulates Islet α-Cell Function by Reducing KATP Channel Sensitivity to Adenosine 5′-Triphosphate Inhibition

Endocrinology ◽  
2006 ◽  
Vol 147 (5) ◽  
pp. 2155-2162 ◽  
Author(s):  
Yuk M. Leung ◽  
Ishtiaq Ahmed ◽  
Laura Sheu ◽  
Xiaodong Gao ◽  
Manami Hara ◽  
...  
Keyword(s):  
Katp Channel ◽  
Cell Function ◽  
Fluorescent Protein ◽  
Glucagon Secretion ◽  
Katp Channels ◽  
Β Cell ◽  
Major Mechanism ◽  
Insulin Promoter ◽  
Atp Inhibition ◽  
Green Fluorescent

Glucose regulates pancreatic islet α-cell glucagon secretion directly by its metabolism to generate ATP in α-cells, and indirectly via stimulation of paracrine release of β-cell secretory products, particularly insulin. How the cellular substrates of these pathways converge in the α-cell is not well known. We recently reported the use of the MIP-GFP (mouse insulin promoter-green fluorescent protein) mouse to reliably identify islet α- (non-green cells) and β-cells (green cells), and characterized their ATP-sensitive K+ (KATP) channel properties, showing that α-cell KATP channels exhibited a 5-fold higher sensitivity to ATP inhibition than β-cell KATP channels. Here, we show that insulin exerted paracrine regulation of α-cells by markedly reducing the sensitivity of α-cell KATP channels to ATP (IC50 = 0.18 and 0.50 mm in absence and presence of insulin, respectively). Insulin also desensitized β-cell KATP channels to ATP inhibition (IC50 = 0.84 and 1.23 mm in absence and presence of insulin, respectively). Insulin effects on both islet cell KATP channels were blocked by wortmannin, indicating that insulin acted on the insulin receptor-phosphatidylinositol 3-kinase signaling pathway. Insulin did not affect α-cell A-type K+ currents. Glutamate, known to also inhibit α-cell glucagon secretion, did not activate α-cell KATP channel opening. We conclude that a major mechanism by which insulin exerts paracrine control on α-cells is by modulating its KATP channel sensitivity to ATP block. This may be an underlying basis for the proposed sequential glucose-insulin regulation of α-cell glucagon secretion, which becomes distorted in diabetes, leading to dysregulated glucagon secretion.

Acetylcholine mimics ischemic preconditioning via a glibenclamide-sensitive mechanism in dogs

1993 ◽  
Vol 264 (6) ◽  
pp. H2221-H2225 ◽  
Author(s):  
Z. Yao ◽  
G. J. Gross
Keyword(s):  
Blood Flow ◽  
Ischemic Preconditioning ◽  
Katp Channel ◽  
Channel Blocker ◽  
Katp Channels ◽  
Protective Effects ◽  
Ischemic Insult ◽  
Area At Risk ◽  
Drug Free

The major objectives of the present study were to examine the ability of acetylcholine (ACh) to mimic ischemic preconditioning in dogs and to determine the role of cardiac ATP-sensitive potassium (KATP) channels in mediating its effects. Barbital-anesthetized open-chest dogs were subjected to 60 min of left anterior descending coronary artery (LAD) occlusion followed by 4 h of reperfusion. Preconditioning was elicited by 10 min of LAD occlusion followed by 10 min of reperfusion before the 60-min occlusion period. ACh (10 micrograms/min) or an equivalent volume of saline were infused into the LAD for 10 min followed by a 10-min drug-free period before the 60-min ischemic insult. In another group, the specific KATP channel blocker glibenclamide (0.3 mg/kg iv) was given 15 min before ACh administration. Transmural myocardial blood flow was measured at 30 min of occlusion, and infarct size (IS) was determined by triphenyltetrazolium staining and expressed as a percentage of the anatomic area at risk (AAR). There were no significant differences in hemodynamics, collateral blood flow, or AAR between groups. Preconditioning produced a marked reduction (P < 0.05) in IS (5.3 +/- 3.0 vs. 23.7 +/- 5.9% in the controls). ACh, similar to preconditioning, resulted in a dramatic decrease in IS (10.0 +/- 2.9%), whereas glibenclamide completely abolished its protective effects (20.9 +/- 4.8%). These results are the first to indicate that ACh mimics ischemic preconditioning via a cardiac KATP channel-sensitive mechanism in dogs.

scholarly journals Regulation of Glucagon Secretion at Low Glucose Concentrations: Evidence for Adenosine Triphosphate-Sensitive Potassium Channel Involvement

Endocrinology ◽  
2005 ◽  
Vol 146 (12) ◽  
pp. 5514-5521 ◽  
Author(s):  
Alvaro Muñoz ◽  
Min Hu ◽  
Khalid Hussain ◽  
Joseph Bryan ◽  
Lydia Aguilar-Bryan ◽  
...  
Keyword(s):  
Inverse Correlation ◽  
Glucagon Secretion ◽  
Katp Channels ◽  
Hepatic Glycogen ◽  
Glucagon Release ◽  
Cell Secretion ◽  
Cellular Mechanisms ◽  
Low Glucose

Glucagon is a potent counterregulatory hormone that opposes the action of insulin in controlling glycemia. The cellular mechanisms by which pancreatic α-cell glucagon secretion occurs in response to hypoglycemia are poorly known. SUR1/KIR6.2-type ATP-sensitive K+ (KATP) channels have been implicated in the glucagon counterregulatory response at central and peripheral levels, but their role is not well understood. In this study, we examined hypoglycemia-induced glucagon secretion in vitro in isolated islets and in vivo using Sur1KO mice lacking neuroendocrine-type KATP channels and paired wild-type (WT) controls. Sur1KO mice fed ad libitum have normal glucagon levels and mobilize hepatic glycogen in response to exogenous glucagon but exhibit a blunted glucagon response to insulin-induced hypoglycemia. Glucagon release from Sur1KO and WT islets is increased at 2.8 mmol/liter glucose and suppressed by increasing glucose concentrations. WT islets increase glucagon secretion approximately 20-fold when challenged with 0.1 mmol/liter glucose vs. approximately 2.7-fold for Sur1KO islets. Glucagon release requires Ca2+ and is inhibited by nifedipine. Consistent with a regulatory interaction between KATP channels and intra-islet zinc-insulin, WT islets exhibit an inverse correlation between β-cell secretion and glucagon release. Glibenclamide stimulated insulin secretion and reduced glucagon release in WT islets but was without effect on secretion from Sur1KO islets. The results indicate that loss of α-cell KATP channels uncouples glucagon release from inhibition by β-cells and reveals a role for KATP channels in the regulation of glucagon release by low glucose.

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