scholarly journals A role for calcium in the breakdown of inositol phospholipids in intact and digitonin-permeabilized pancreatic islets

1986 ◽  
Vol 238 (3) ◽  
pp. 773-779 ◽  
Author(s):  
L Best
Keyword(s):  
Lipid Metabolism ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Islet Cells ◽  
Inositol Phosphate ◽  
Significant Stimulation ◽  
Inositol Phospholipids ◽  
Inositol Phosphate Production ◽  
Small Inhibition ◽  
Stimulation Of

Glucose (20 mM) and 4-methyl-2-oxopentanoate (10 mM) both caused a pronounced stimulation of insulin release and of [3H]inositol phosphate production in rat pancreatic islets prelabelled with myo-[3H]inositol. Secretory responses to these nutrients were markedly impaired by lowering the Ca2+ concentration of the incubation medium to 10(-4)M or less, whereas stimulated inositol phosphate production was sensitive to Ca2+ within the range 10(-6)-10(-4)M. Inositol phosphate formation in response to carbamoylcholine was also found to be dependent on the presence of 10(-5)M-Ca2+ or above. Raising the concentration of K+ in the medium resulted in a progressive, Ca2+-dependent stimulation of inositol phosphate production in islets, although no significant stimulation of insulin release was observed. In islets prelabelled with myo[3H]inositol, then permeabilized by exposure to digitonin, [3H]inositol phosphate production could be triggered by raising the Ca2+ concentration from 10(-7) to 10(-5)M. This effect was dependent on the concentration of ATP and the presence of Li+, and involved detectable increases in the levels of InsP3 and InsP2 as well as InsP. A potentiation of inositol phosphate production by carbamoylcholine was observed in permeabilized islets at lower Ca2+ concentrations, although nutrient stimuli were ineffective. No significant effects were observed with guanine nucleotides or with neomycin, although NADH produced a modest increase and adriamycin a small inhibition of inositol phosphate production in permeabilized islets. These results strongly suggest that Ca2+ ions play an important role in the stimulation of inositol lipid metabolism in islets in response to nutrient secretagogues, and that inositide breakdown may actually be triggered by Ca2+ entry into the islet cells.

scholarly journals Changes in free cytosolic calcium and accumulation of inositol phosphates in isolated hepatocytes by [Leu]enkephalin

1986 ◽  
Vol 238 (2) ◽  
pp. 537-542 ◽  
Author(s):  
R P Leach ◽  
S B Shears ◽  
C J Kirk ◽  
M A Titheradge
Keyword(s):  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Cytosolic Calcium ◽  
Isolated Hepatocytes ◽  
Opioid Peptide ◽  
Alpha Activity ◽  
Dose Dependency ◽  
Significant Stimulation ◽  
Inositol Phosphate Production ◽  
Stimulation Of

Isolated hepatocytes from fed rats were used to study the effects of the opioid peptide [Leu]enkephalin on intracellular free cytosolic Ca2+ ([Ca2+]i) and inositol phosphate production. By measuring the fluorescence of the intracellular Ca2+-selective indicator quin-2, [Leu]enkephalin was found to increase [Ca2+]i rapidly from a resting value of 0.219 microM to 0.55 microM. The magnitude of this response was comparable with that produced by maximally stimulating concentrations of either vasopressin (100 nM) or phenylephrine (10 microM). The opioid-peptide-mediated increase in [Ca2+]i showed a dose-dependency comparable with the activation of phosphorylase, but it preceded the increase in phosphorylase alpha activity. Addition of [Leu]enkephalin to hepatocytes prelabelled with myo-[2-3H(n)]inositol resulted in a significant stimulation of inositol phosphate production. At 10 min after hormone addition, there were increases in the concentrations of inositol mono-, bis- and tris-phosphate fractions of 12-, 9- and 14-fold respectively. No effect was apparent on the glycerophosphoinositol fraction. The effect of 10 microM-[Leu]enkephalin on inositol phosphate production was significantly greater than that obtained with 10 microM-phenylephrine, but marginally smaller than that induced by 100 nM-vasopressin. However, at these concentrations all three agonists gave a comparable increase in [Ca2+]i and activation of phosphorylase a. These data provide evidence for [Leu]enkephalin acting via a mechanism involving a mobilization of Ca2+ as a result of increased phosphatidylinositol turnover.

scholarly journals Mechanisms of the stimulation of insulin release by oxytocin in normal mouse islets

1991 ◽  
Vol 276 (1) ◽  
pp. 169-174 ◽  
Author(s):  
Z Y Gao ◽  
G Drews ◽  
J C Henquin
Keyword(s):  
B Cells ◽  
Cyclic Amp ◽  
Insulin Release ◽  
Islet Cells ◽  
Inositol Phosphate ◽  
Resting Potential ◽  
Phosphoinositide Metabolism ◽  
Mouse Islets ◽  
45Ca Efflux ◽  
Stimulation Of

Oxytocin (OT) produced a dose-dependent increase in somatostatin, glucagon and insulin release by isolated mouse islets. A small effect on somatostatin release was observed with 0.1 nM-OT, but 1-10 nM-OT was required to affect A- and B- cells significantly. The effects of OT on somatostatin and glucagon release were similar in the presence of 3 mM- and 10 mM-glucose. No change in insulin release was produced by OT in 3 mM-glucose, but a stimulation was still observed in the presence of a maximally effective concentration of glucose (30 mM). The increase in insulin release produced by OT (in 15 mM-glucose) was accompanied by small accelerations of 86Rb and 45Ca efflux from islet cells. Omission of extracellular Ca2+ accentuated the effect of OT on 86Rb efflux, attenuated that on 45Ca efflux, and abolished that on release. OT never inhibited 86Rb efflux. It did not affect the resting potential of B-cells, but slightly increased the Ca2(+)-dependent electrical activity induced by 15 mM-glucose. OT did not affect cyclic AMP levels, but increased inositol phosphate levels in islet cells. It is suggested that the amplification of glucose-induced insulin release that OT produces is due to a stimulation of phosphoinositide metabolism, and presumably an activation of protein kinase C, rather than to a change in cyclic AMP levels or a direct action on the membrane potential. Since OT is present in the pancreas, it is possible that it exerts a neuropeptidergic control of the islet function.

Impairment by aminooxyacetate of ionic response to nutrients in pancreatic islets

1983 ◽  
Vol 245 (1) ◽  
pp. E38-E46
Author(s):  
P. Lebrun ◽  
W. J. Malaisse ◽  
A. Herchuelz
Keyword(s):  
Pancreatic Islets ◽  
Insulin Release ◽  
Redox State ◽  
Islet Cells ◽  
Inhibitory Effect ◽  
High Concentration ◽  
Perifused Islets ◽  
45Ca Efflux ◽  
Reduced State ◽  
Stimulation Of

Aminooxyacetate, an inhibitor of transamination reactions, was recently reported to prevent the induction of a more reduced state in the cytosolic redox couple, as normally evoked by glucose or 2-ketoisocaproate in rat pancreatic islets. The cationic effects of aminooxyacetate were examined, therefore, in perifused islets prelabeled with either 86Rb or 45Ca. Aminooxyacetate augmented the outflow of 86Rb from the islets whether in the absence or presence of an exogenous nutrient and slightly impaired the capacity of nutrients, especially 2-ketoisocaproate, to decrease 86Rb outflow. Aminooxyacetate abolished the nutrient-induced rise in 45Ca efflux that normally results from the stimulation by glucose or 2-ketoisocaproate of 40Ca influx into the islet cells. Aminooxyacetate, however, failed to suppress the early inhibitory effect of nutrients on 45Ca efflux. The alteration by aminooxyacetate of the cationic response to nutrient secretagogues coincided with a suppression of insulin release, whereas the cationic response to a nonnutrient stimulation by a high concentration of extracellular K+ was unaffected by aminooxyacetate. These findings suggest that the induction of a more reduced cytosolic redox state represents an essential link between metabolic events and both the decrease in K+ conductance and stimulation of Ca2+ inflow in the process of nutrient-induced insulin release.

Effects of l-leucine, its 2-keto acid metabolite and its nonmetabolized analogue on rat tumoral islet cell function

1988 ◽  
Vol 1 (1) ◽  
pp. 69-76 ◽  
Author(s):  
V. Leclercq-Meyer ◽  
J. Marchand ◽  
A. Sener ◽  
F. Blachier ◽  
W. J. Malaisse
Keyword(s):  
Insulin Release ◽  
Cell Function ◽  
Islet Cells ◽  
Adenine Nucleotides ◽  
Secretory Response ◽  
Acid Metabolite ◽  
Dual Effect ◽  
Islet Cell Function ◽  
Insulinoma Cells ◽  
Stimulation Of

ABSTRACT l-Leucine and 2-ketoisocaproate stimulated insulin release from perifused rat tumoral islet cells (RINm5F line). The secretory response coincided with an increase in the intracellular ATP/ADP ratio, a stimulation of 45Ca outflow from cells perifused in the presence of extracellular Ca2+, and an increase in 32P efflux from cells prelabelled with radioactive orthophosphate. In contrast to d-glucose, however, l-leucine or 2-ketoisocaproate failed to decrease 86Rb outflow, to inhibit 45Ca outflow from cells perifused in the absence of Ca2+ and to enhance the labelling of inositol-containing phospholipids in cells exposed to myo-[2-3H]inositol. These findings suggest that d-glucose, l-leucine and 2-ketoisocaproate exert dissimilar effects on the subcellular distribution of adenine nucleotides and/or 86Rb. The nonmetabolized analogue of l-leucine, 2-aminobicyclo-[2.2.1]heptane-2-carboxylic acid (BCH), also caused an initial stimulation of insulin release and 32P efflux, but this was soon followed by a severe and irreversible inhibition of insulin output, associated with a permanent enhancement of 86Rb outflow. The dual ionic and secretory response to BCH is interpreted in the light of its dual effect on the catabolism of endogenous amino and fatty acids, and raises the view that BCH could be used to interfere with the function of insulinoma cells.

Direct effect of parathyroid hormone on insulin secretion from pancreatic islets

1990 ◽  
Vol 258 (6) ◽  
pp. E975-E984 ◽  
Author(s):  
G. Z. Fadda ◽  
M. Akmal ◽  
L. G. Lipson ◽  
S. G. Massry
Keyword(s):  
Insulin Secretion ◽  
Parathyroid Hormone ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Direct Effect ◽  
Indirect Evidence ◽  
Cytosolic Calcium ◽  
Dependent Manner ◽  
Stimulation Of

Indirect evidence indicates that parathyroid hormone (PTH) interacts with pancreatic islets and modulates their insulin secretion. This property of PTH has been implicated in the genesis of impaired insulin release in chronic renal failure. We examined the direct effect of PTH-(1-84) and PTH-(1-34) on insulin release using in vitro static incubation and dynamic perifusion of pancreatic islets from normal rats. Both moieties of the hormone stimulated in a dose-dependent manner glucose-induced insulin release but higher doses inhibited glucose-induced insulin release. This action of PTH was modulated by the calcium concentration in the media. The stimulatory effect of PTH was abolished by its inactivation and blocked by its antagonist [Tyr-34]bPTH-(7-34)NH2. PTH also augmented phorbol ester (TPA)-induced insulin release, stimulated adenosine 3',5'-cyclic monophosphate (cAMP) generation by pancreatic islets, and significantly increased (+50 +/- 2.7%, P less than 0.01) their cytosolic calcium. Verapamil inhibited the stimulatory effect of PTH on insulin release. The data show that 1) pancreatic islets are a PTH target and may have PTH receptors, 2) stimulation of glucose-induced insulin release by PTH is mediated by a rise in cytosolic calcium, 3) stimulation of cAMP production by PTH and a potential indirect activation of protein kinase C by PTH may also contribute to the stimulatory effect on glucose-induced insulin release, and 4) this action of PTH requires calcium in incubation or perifusion media.

Sensitivity to Cd2+ but resistance to Ni2+ of Ca2+ inflow into rat pancreatic islets

1990 ◽  
Vol 258 (3) ◽  
pp. E529-E533 ◽  
Author(s):  
P. O. Plasman ◽  
M. Hermann ◽  
A. Herchuelz ◽  
P. Lebrun
Keyword(s):  
Pancreatic Islets ◽  
Insulin Release ◽  
Islet Cells ◽  
Excitable Cells ◽  
45Ca Uptake ◽  
Rat Pancreatic Islets ◽  
Cell Plasma ◽  
Different Types ◽  
45Ca Efflux ◽  
Ca2 Channels

The presence of different types [long lasting (L) and transient (T)] of active voltage-operated Ca2+ channels in islet cells was investigated by comparing the effects of Cd2+, Ni2+, and 1,4-dihydropyridines on 45Ca uptake, 45Ca efflux, and insulin release in intact rat pancreatic islets. In several other excitable cells the L-channel has been shown to be modulated by 1,4-dihydropyridines and Cd2+, whereas the T-channel was reported to be sensitive to Ni2+. Nifedipine and Cd2+ inhibited whereas BAY K 8644 enhanced the glucose (11.1, 22.2 mM)-stimulated short-term 45Ca uptake, 45Ca efflux, and insulin release. In contrast, the stimulatory effects of glucose (11.1, 22.2 mM) on 45Ca uptake, 45Ca efflux, and insulin release were unaffected by Ni2+. These findings confirm that glucose provokes Ca2+ entry mainly by activating voltage-sensitive Ca2+ channels of the L-type and suggest that the B-cell plasma membrane is not equipped with active T-type Ca2+ channels.

Mechanisms of synergism between glucose and cAMP on stimulation of insulin release

1984 ◽  
Vol 247 (6) ◽  
pp. E701-E708 ◽  
Author(s):  
W. Phang ◽  
L. Domboski ◽  
Y. Krausz ◽  
G. W. Sharp
Keyword(s):  
Pancreatic Islets ◽  
Insulin Release ◽  
Ringer Solution ◽  
Intracellular Camp ◽  
Cyclic Monophosphate ◽  
Rat Pancreatic Islets ◽  
Individual Effects ◽  
The Individual ◽  
Isolated Rat ◽  
Stimulation Of

The mechanism of synergism between glucose and adenosine 3',5'-cyclic monophosphate (cAMP) on insulin release has been studied. Synergism may result from 1) inhibition of Na+-Ca2+ exchange by glucose and 2) a cAMP-induced sensitization of the release machinery to Ca2+. To distinguish between these two possibilities, isolated rat pancreatic islets were perifused with agents that raise intracellular levels of cAMP [3-isobutyl-1-methylxanthine (IBMX) and forskolin] and others that increase intracellular concentrations of Ca2+ either by blocking Na2+-Ca2+ exchange (ouabain and choline-Ringer solution) or by causing increased Ca2+ influx (KCl, carbachol, and 10 mM Ca2+). The results indicate that both the combination of cAMP and increased Ca2+ influx or blocked Na2-Ca2+ exchange and increased Ca2+ influx potentiated insulin release. When the relative potentiating abilities of cAMP and blocked Na2+-Ca2+ exchange were compared by determining the individual effects of IBMX and 1 mM ouabain (a concentration that causes similar inhibition of 45C2+ efflux as 16.7 mM glucose) in the presence of carbachol, cAMP was only 1.4 times more potent as a potentiating agent than blocked Na+-Ca2+ exchange. The greatest potentiation of insulin release was observed when Na+-Ca2+ exchange was blocked in the presence of increased levels of intracellular cAMP.

scholarly journals Divergent roles for ferric ions in the biological activity of amidated and non-amidated gastrins

2004 ◽  
Vol 181 (2) ◽  
pp. 315-325 ◽  
Author(s):  
J Pannequin ◽  
JP Tantiongco ◽  
S Kovac ◽  
A Shulkes ◽  
GS Baldwin
Keyword(s):  
Biological Activity ◽  
Inositol Phosphate ◽  
Peptide Hormone ◽  
Iron Chelator ◽  
Spectroscopic Studies ◽  
Jurkat Cells ◽  
Ferric Ion ◽  
Ferric Ions ◽  
Inositol Phosphate Production ◽  
Stimulation Of

Amidated forms of the peptide hormone gastrin act via the cholecystokinin-2 receptor to stimulate gastric acid secretion, whereas non-amidated forms stimulate colonic mucosal proliferation via a novel, as yet uncharacterised, receptor. Nuclear magnetic resonance (NMR) and fluorescence spectroscopic studies have revealed that glycine-extended gastrin17 bound two ferric ions, and that ferric ion binding was essential for biological activity. We have therefore investigated the role of ferric ions in the biological activity of amidated gastrin17. As with glycine-extended gastrin17, fluorescence quenching experiments indicated that Glu7 Ala and Glu8,9 Ala mutants of amidated gastrin17 each bound only one ferric ion. The affinity of the mutant peptides for the cholecystokinin-2 receptor on transfected COS-7 cells or on Tlymphoblastoid Jurkat cells, and their potency in stimulation of proliferation in Jurkat cells and inositol phosphate production in transfected COS-7 cells, were similar to the values obtained for amidated gastrin17. In addition, the iron chelator desferrioxamine did not significantly inhibit either binding of amidated gastrin17 to the cholecystokinin-2 receptor, or stimulation of inositol phosphate production by amidated gastrin17 in transfected COS-7 cells. We conclude that, in contrast to glycine-extended gastrin17, binding of ferric ions is not essential for the biological activity of amidated gastrin17. Our results support the concept of distinct modes of action for amidated and non-amidated gastrins, and raise the possibility of developing selective antagonists of the actions of non-amidated and amidated gastrins.

Sign in / Sign up

Export Citation Format

Share Document