The Adenylyl Cyclase Inhibitor MDL-12,330A Potentiates Insulin Secretion via Blockade of Voltage-Dependent K+ Channels in Pancreatic Beta Cells

The role(s) played by protein tyrosine kinases (PTKs) in the regulation of insulin secretion from pancreatic beta cells is not clear. We have examined the effects of glucose, the major physiological insulin secretagogue, on the tyrosine phosphorylation state of islet proteins, and assessed beta cell insulin secretory responses in the presence of PTK inhibitors. Under basal conditions islets contained many proteins phosphorylated on tyrosine residues, and glucose (20 mM; 5-15 min) was without demonstrable effect on the pattern of tyrosine phosphorylation, in either the absence or presence of the protein tyrosine phosphatase (PTP) inhibitor, sodium pervanadate (PV). PV alone (100 microM) increased tyrosine phosphorylation of several islet proteins. The PTK inhibitors genistein (GS) and tyrphostin A47 (TA47) inhibited islet tyrosine kinase activities and glucose-, 4alpha ketoisocaproic acid (KIC)- and sulphonylurea-stimulated insulin release, without affecting glucose metabolism. GS and TA47 also inhibited protein serine/threonine kinase activities to a limited extent, but had no effect on Ca2+, cyclic AMP- or phorbol myristate acetate (PMA)-induced insulin secretion from electrically permeabilised islets. These results suggest that PTK inhibitors exert their inhibitory effects on insulin secretion proximal to Ca2+ entry and it is proposed that they act at the site of the voltage-dependent Ca2+ channel which regulates Ca2+ influx into beta cells following nutrient- and sulphonylurea-induced depolarisation.

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Potential role of adenylyl cyclase 8 signaling complexes in regulating insulin secretion from pancreatic beta cells

Cellular Signalling ◽

10.1016/j.cellsig.2020.109635 ◽

2020 ◽

Vol 72 ◽

pp. 109635

Author(s):

Ida Lønsmann ◽

Lasse K. Bak

Keyword(s):

Insulin Secretion ◽

Adenylyl Cyclase ◽

Beta Cells ◽

Pancreatic Beta Cells ◽

Potential Role ◽

Adenylyl Cyclase 8

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Delayed rectifying and calcium-activated K+ channels and their significance for action potential repolarization in mouse pancreatic beta-cells.

The Journal of General Physiology ◽

10.1085/jgp.95.6.1041 ◽

1990 ◽

Vol 95 (6) ◽

pp. 1041-1059 ◽

Cited By ~ 64

Author(s):

P A Smith ◽

K Bokvist ◽

P Arkhammar ◽

P O Berggren ◽

P Rorsman

Keyword(s):

Beta Cells ◽

Action Potentials ◽

Pancreatic Beta Cells ◽

Single Channel ◽

Outward Current ◽

K Channel ◽

K Channels ◽

Dependent Component ◽

Voltage Dependent ◽

Action Potential Repolarization

The contribution of Ca2(+)-activated and delayed rectifying K+ channels to the voltage-dependent outward current involved in spike repolarization in mouse pancreatic beta-cells (Rorsman, P., and G. Trube. 1986. J. Physiol. 374:531-550) was assessed using patch-clamp techniques. A Ca2(+)-dependent component could be identified by its rapid inactivation and sensitivity to the Ca2+ channel blocker Cd2+. This current showed the same voltage dependence as the voltage-activated (Cd2(+)-sensitive) Ca2+ current and contributed 10-20% to the total beta-cell delayed outward current. The single-channel events underlying the Ca2(+)-activated component were investigated in cell-attached patches. Increase of [Ca2+]i invariably induced a dramatic increase in the open state probability of a Ca2(+)-activated K+ channel. This channel had a single-channel conductance of 70 pS [( K+]o = 5.6 mM). The Ca2(+)-independent outward current (constituting greater than 80% of the total) reflected the activation of an 8 pS [( K+]o = 5.6 mM; [K+]i = 155 mM) K+ channel. This channel was the only type observed to be associated with action potentials in cell-attached patches. It is suggested that in mouse beta-cells spike repolarization results mainly from the opening of the 8-pS delayed rectifying K+ channel.

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Rebaudioside A directly stimulates insulin secretion from pancreatic beta cells: a glucose-dependent action via inhibition of ATP-sensitive K+-channels*

Diabetes Obesity and Metabolism ◽

10.1111/j.1463-1326.2008.00864.x ◽

2008 ◽

Vol 10 (11) ◽

pp. 1074-1085 ◽

Cited By ~ 26

Author(s):

R. Abudula ◽

V. V. Matchkov ◽

P. B. Jeppesen ◽

H. Nilsson ◽

C. Aalkjaer ◽

...

Keyword(s):

Insulin Secretion ◽

Beta Cells ◽

Pancreatic Beta Cells ◽

Rebaudioside A ◽

K Channels

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Nitric oxide opens ATP-sensitive K+ channels through suppression of phosphofructokinase activity and inhibits glucose-induced insulin release in pancreatic beta cells.

The Journal of General Physiology ◽

10.1085/jgp.104.6.1079 ◽

1994 ◽

Vol 104 (6) ◽

pp. 1079-1098 ◽

Cited By ~ 56

Author(s):

Y Tsuura ◽

H Ishida ◽

S Hayashi ◽

K Sakamoto ◽

M Horie ◽

...

Keyword(s):

Nitric Oxide ◽

Insulin Secretion ◽

Beta Cells ◽

Katp Channel ◽

Pancreatic Beta Cells ◽

Katp Channels ◽

Channel Activity ◽

K Channels ◽

Intracellular Mechanism ◽

Phosphofructokinase Activity

Nitric oxide (NO) is known to be a potent messenger in the intracellular signal transduction system in many tissues. In pancreatic beta cells, NO has been reported to be formed from L-arginine through NO synthase. To elucidate the effect of NO on insulin secretion and to investigate the intracellular mechanism of its effect, we have used sodium nitroprusside (SNP) as a NO donor. SNP inhibited glucose-induced insulin secretion in a dose-dependent manner, and its effect was reversed by hemoglobin, a known NO scavenger. However, glyceraldehyde-induced insulin secretion was not affected by SNP. Since the closure of ATP-sensitive K+ channels (KATP channel) has been established as a key step in glucose-induced insulin secretion, we have directly assessed the effect of SNP on KATP channel activity using the patch clamp technique. The KATP channel activity reduced by glucose was found to be reversibly activated by the addition of SNP, and this activation was able to be similarly reproduced by applying S-Nitroso-N-acetyl-DL-penicillamine (SNAP), another NO generator. Furthermore, these activating effects were completely eliminated by hemoglobin, in accordance with the reversibility in inhibition of glucose-induced insulin release. However, SNP could not affect the KATP channel suppression by ATP applied to the inside of the plasma membrane. The activation of the KATP channel by NO, therefore, seems to be due to the decreased ATP production attributable to impairment of glucose metabolism in beta cells. Since SNP exhibited no effect on glyceraldehyde-induced KATP channel inhibition, NO may disturb a glycolytic step before glyceraldehyde-3-phosphate. The KATP channel activation by 2-deoxyglucose through presumable ATP consumption due to its phosphorylation by glucokinase was, however, not affected even in the presence of SNP. But in the permeabilized beta cells made by exposure to a low concentration (0.02 U/ml) of streptolysin O (open cell-attached configuration), SNP reopens KATP channels which have been eliminated by fructose-6-phosphate, while this effect was not observed in the KATP channels inhibited by fructose-1,6-bisphosphate. On the other hand, in rat ventricular myocyte KATP channels were not activated by SNP even under a low concentration of glucose. From these observations, the inhibition of phosphofructokinase activity is probably the site responsible for the impairment of glucose metabolism induced by NO in pancreatic beta cells. NO, therefore, seems to be a factor in the deterioration of glucose-induced insulin secretion from pancreatic beta cells through a unique intracellular mechanism.

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Stimulation of arterial 42K efflux by ATP depletion and cromakalim is antagonized by glyburide

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1991.260.3.h848 ◽

1991 ◽

Vol 260 (3) ◽

pp. H848-H854

Author(s):

J. M. Post ◽

A. W. Jones

Keyword(s):

Smooth Muscle ◽

Vascular Smooth Muscle ◽

Beta Cells ◽

Pancreatic Beta Cells ◽

High Performance ◽

Atp Depletion ◽

Mesenteric Arteries ◽

K Channels ◽

Voltage Dependent ◽

Stimulation Of

It has been suggested that cromakalim (BRL 34915)-induced vasorelaxation was associated with stimulation of ATP-sensitive K channels. The hyperpolarization resulting from activation of this mechanism might then inhibit voltage-dependent Ca2+ entry and subsequent contraction. The present study evaluated the similarities of 42K efflux stimulated by ATP depletion (verified by high-performance liquid chromatography) and by exposure to cromakalim (10 microM) in rabbit superior mesenteric arteries. Both depletion of intracellular ATP and exposure to cromakalim significantly stimulated 42K efflux (P less than 0.05). Glyburide (a selective inhibitor of ATP-sensitive K channels in pancreatic beta-cells) inhibited 42K efflux stimulated by ATP depletion and by cromakalim exposure. Glyburide (10 microM) had no significant effect on either basal 42K or the 42K efflux stimulated by norepinephrine and by K depolarization, which cause voltage and Ca2(+)-dependent activation of K channels. Glyburide therefore had a relatively selective effect on vascular smooth muscle. The glyburide-sensitive 42K efflux during ATP depletion and exposure to cromakalim was greatest in Ca2(+)-free solution (Mg raised to 10 mM). We conclude that in vascular smooth muscle both depletion of ATP and exposure to cromakalim stimulate 42K efflux via a glyburide-sensitive mechanism with properties similar to those of ATP-sensitive K channels observed in cardiac and pancreatic beta-cells.

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