Stimulation of insulin secretion from isolated rat islets of Langerhans by melittin

1984 ◽  
Vol 4 (8) ◽  
pp. 665-671 ◽  
Author(s):  
Noel G. Morgan ◽  
William Montague
Keyword(s):  
Insulin Secretion ◽  
Islets Of Langerhans ◽  
Maximal Response ◽  
Secretory Rate ◽  
Rat Islets ◽  
Cell Plasma ◽  
Rat Islets Of Langerhans ◽  
Dose Dependent ◽  
Stimulation Of

Melittin, an amphipathic polypeptide, stimulated the secretion of insulin from rat islets of Langerhans incubated in vitro. The secretory response was dose-dependent and saturable with half the maximal response elicited by a melittin concentration of 4 μg/ml. The response was rapid in onset, an increase in secretion occurring within 2 rain of exposure of the islets to melittin (2 μg/ml). An enhanced secretory rate could be maintained for at least 40 rain in the presence of melittin but declined steadily when the agent was removed. Stimulation of secretion by melittin occurred in the absence of glucose and in the presence of both 4 mM and 8 mM glucose but not in the presence of 20 mM glucose. The effect of melittin on secretion was dependent on the presence of extracellular calcium but was not inhibited by norepinephrine. The data suggest that melittin may be a valuable agent for further study of the role played by the B-cell plasma membrane in the regulation of insulin secretion.

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.

Russell's viper venom stimulates insulin secretion from rat islets of Langerhans

1993 ◽  
Vol 136 (1) ◽  
pp. 27-33 ◽  
Author(s):  
P. M. Jones ◽  
F. M. Mann
Keyword(s):  
Insulin Secretion ◽  
Islets Of Langerhans ◽  
Prolonged Exposure ◽  
Blue Dye ◽  
Dependent Inhibition ◽  
Dose Dependent Inhibition ◽  
Russell’S Viper ◽  
Rat Islets Of Langerhans ◽  
Dose Dependent ◽  
Stimulation Of

ABSTRACT Burmese Russell's viper venom (RVV) caused a dose-and temperature-dependent stimulation of insulin secretion from islets of Langerhans isolated from rat pancreas by collagenase digestion. RVV stimulated both basal and glucose-induced insulin secretion at concentrations which did not compromise islet cell viability as assessed by exclusion of trypan blue dye. The effects of RVV on insulin secretion could not be attributed to the activation of protein kinase C (PKC), since down-regulation of PKC by prolonged exposure to a tumour-promoting phorbol ester did not abolish subsequent secretory responses to RVV. However, RVV-induced insulin secretion was inhibited in the absence of extracellular Ca2 +, and RVV did not stimulate insulin secretion from Ca2+-clamped electrically permeabilized islets at either substimulatory (50 nmol/l) or stimulatory (10 μmol/l) concentrations of Ca2 +, suggesting that changes in cytosolic Ca2+ are important in the stimulation of insulin secretion by RVV. The phospholipase A2 (PLA2) inhibitor quinacrine caused a dose-dependent inhibition of RVV-induced insulin secretion, suggesting that the activation of PLA2, perhaps in response to Ca2+ influx, may be partially responsible for RVV-induced insulin secretion. Journal of Endocrinology (1993) 136, 27–33

scholarly journals Mechanisms involved in intracellular calcium mobilization in isolated rat islets of Langerhans

1987 ◽  
Vol 244 (3) ◽  
pp. 669-674 ◽  
Author(s):  
N G Morgan ◽  
G M Rumford ◽  
W Montague
Keyword(s):  
Arachidonic Acid ◽  
Islets Of Langerhans ◽  
Inositol Trisphosphate ◽  
Arachidonic Acid Content ◽  
Dependent Manner ◽  
Amphipathic Peptide ◽  
Rat Islets ◽  
Rat Islets Of Langerhans ◽  
Dose Dependent ◽  
Stimulation Of

1. The rate of 45Ca2+ efflux from prelabelled rat islets of Langerhans was stimulated by carbachol in a dose-dependent manner. 2. Significant stimulation occurred in the presence of 0.2 microM-carbachol; the response was half-maximal at 3-5 microM and was maximal at 20 microM. 3. Stimulation of 45Ca2+ efflux by carbachol was not dependent on the presence of extracellular Ca2+ and was enhanced in Ca2+-depleted medium. 4. Stimulation of 45Ca2+ efflux by 5 microM-carbachol occurred independently of any change in [3H]arachidonic acid release in prelabelled islets, and probably reflected generation of inositol trisphosphate in the cells. 5. The amphipathic peptide melittin failed to increase islet-cell 45Ca2+ efflux at a concentration of 1 microgram/ml, and caused only a modest increase at 10 micrograms/ml. 6. Despite its failure to increase 45Ca2+ efflux, melittin at 1 microgram/ml caused a marked enhancement of 3H release from islets that had been prelabelled with [3H]arachidonic acid. 7. The stimulation of 3H efflux caused by melittin correlated with a dose-dependent increase in the unesterified [3H]arachidonic acid content of prelabelled islets and with a corresponding decrease in the extent of labelling of islet phospholipids. 8. Combined addition of melittin (1 microgram/ml) and 5 microM-carbachol to perifused islets failed to augment 45Ca2+ efflux relative to that elicited by carbachol alone. 9. The data indicate that melittin promotes an increase in arachidonic acid availability in intact rat islets. They do not, however, support the proposal that this can either directly reproduce or subsequently modify the extent of intracellular Ca2+ mobilization induced by agents that cause an increase in inositol trisphosphate.

scholarly journals Regulation of actin polymerizaton in rat islets of Langerhans

1980 ◽  
Vol 192 (1) ◽  
pp. 381-383 ◽  
Author(s):  
S L Howell ◽  
M Tyhurst
Keyword(s):  
Insulin Secretion ◽  
Islets Of Langerhans ◽  
Subcellular Fractionation ◽  
Inhibition Assay ◽  
Rat Islets ◽  
Rat Islets Of Langerhans ◽  
Stimulation Of

A DNAase-inhibition assay was used to determine the proportions of globular (G-) and filamentous (F-) actin in islets of Langerhans after incubation in various conditions, or after subcellular fractionation. Stimulation of insulin secretion resulted in an ATP-dependent increase in the proportion of F-actin present; fractionation showed 80-90% of the actin to be present in the final supernatant.

scholarly journals Effects of the calcium-channel agonist CGP 28392 on insulin secretion from isolated rat islets of Langerhans

1985 ◽  
Vol 231 (3) ◽  
pp. 629-634 ◽  
Author(s):  
N G Morgan ◽  
C D Short ◽  
G M Rumford ◽  
W Montague
Keyword(s):  
Insulin Secretion ◽  
Islets Of Langerhans ◽  
A Value ◽  
Isolated Rat Islets ◽  
Rat Islets Of Langerhans ◽  
Dose Dependent ◽  
Dihydropyridine Derivatives ◽  
Ca2 Channels ◽  
Isolated Rat ◽  
Stimulation Of

The rate of insulin secretion from isolated rat islets of Langerhans was affected by a number of dihydropyridine derivatives known to interact with voltage-sensitive Ca2+ channels in excitable cells. The channel antagonists nifedipine and nitrendipine were potent inhibitors of glucose-induced insulin secretion in response to both 8 mM- and 20 mM-glucose, although they did not lower the basal secretion rate observed in the presence of 4 mM-glucose. The Ca2+-channel agonist, CGP 28392, also failed to alter the basal rate of insulin secretion. In the presence of 8 mM-glucose, however, 1 microM-CGP 28392 enhanced the insulin-secretion rate to a value approximately double that with 8 mM-glucose alone. This effect was dose-dependent, with half the maximal response elicited by 0.1 microM-CGP 28392, and full enhancement at 10 microM. The response was rapid in onset, with an increase in insulin secretion evident within 2 min of CGP 28392 infusion in perifused islets. Stimulation of insulin secretion by CGP 28392 was correlated with a rapid enhancement of glucose-stimulated 45Ca2+ uptake into islets cells, and with a transiently increased rate of 45Ca2+ efflux from pre-loaded islets. Stimulation of insulin secretion by CGP 28392 was abolished in the presence of noradrenaline, although under these conditions the rapid stimulation of 45Ca2+ influx induced by CGP 28392 was only partially inhibited. In contrast with these results, when islets were incubated in the presence of 20 mM-glucose, CGP 28392 caused a dose-dependent inhibition of insulin secretion. Half-maximal inhibition required approx. 0.2 microM-CGP 28392, with maximal effects observed at 10 microM. Under these conditions, however, the extent of insulin secretion was still only decreased by about 50%, to a value which was similar to that seen in the presence of 8 mM-glucose and CGP 28392. These results suggest that dihydropyridine derivatives can alter the activity of voltage-dependent Ca2+ channels in islet cells, and are consistent with the possibility that gating of these channels plays an important role in regulating the rate of insulin secretion after glucose stimulation.

scholarly journals A possible role of adenylate cyclase in the longterm dietary regulation of insulin secretion from rat islets of Langerhans

1973 ◽  
Vol 136 (2) ◽  
pp. 343-349 ◽  
Author(s):  
Simon L. Howell ◽  
Irene C. Green ◽  
William Montague
Keyword(s):  
Insulin Secretion ◽  
Adenylate Cyclase ◽  
Islets Of Langerhans ◽  
Glucose Concentration ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Maximal Response ◽  
Long Term Effects ◽  
Stimulation Of

1. Adenylate cyclase activity and patterns of insulin release in response to various concentrations of glucose were determined in islets of Langerhans isolated from starving, fed, or glucose-loaded rats. 2. Basal and glucagon-stimulated activities of adenylate cyclase were lower in islets from starved than from fed rats. The minimum glucose concentration required for stimulation of insulin secretion was higher, whereas the maximum secretory response to glucose was lower, in islets from starved than from fed rats. 3. Adenylate cyclase activity in islets of Langerhans obtained from fed rats loaded with glucose by intermittent intravenous or intraperitoneal injections over 5h was significantly higher than that seen in islets from normal fed rats. Islets obtained from glucose-loaded rats required a lower glucose concentration for stimulation of insulin secretion and attained a higher maximal response to glucose stimulation than those derived from fed rats. 4. Incubation in vitro of islets isolated from normal fed rats, for periods of 1 to 24h in the presence of high concentrations of glucose resulted in an activation of adenylate cyclase that occurred progressively from 2 to 7h and which was maintained during 24h of incubation. The increase of adenylate cyclase activity in isolated islets incubated for 4h in the presence of glucose was not prevented by addition of cycloheximide or actinomycin D. Galactose or 2-deoxyglucose was ineffective in increasing adenylate cyclase activity, and pyruvate (20mm) was less effective than glucose. 5. It is suggested that glucose or a glucose metabolite may exert long-term effects on islet cell adenylate cyclase.

scholarly journals Stimulation of Adenylate Cyclase by Ca2+ and Calmodulin in Rat Islets of Langerhans: Explanation for the Glucose-induced Increase in Cyclic AMP Levels

Diabetes ◽  
1980 ◽  
Vol 29 (1) ◽  
pp. 74-77 ◽  
Author(s):  
G. W. G. Sharp ◽  
D. E. Wiedenkeller ◽  
D. Kaelin ◽  
E. G. Siegel ◽  
C. B. Wollheim
Keyword(s):  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Islets Of Langerhans ◽  
Rat Islets ◽  
Rat Islets Of Langerhans ◽  
Stimulation Of

Immunoprecipitation of a pertussis toxin substrate of the Go family from rat islets of Langerhans

1992 ◽  
Vol 12 (2) ◽  
pp. 95-100 ◽  
Author(s):  
Nicholas S. Berrow ◽  
Roger D. Hurst ◽  
Susan L. F. Chan ◽  
Noel G. Morgan
Keyword(s):  
Molecular Weight ◽  
Insulin Secretion ◽  
Adenylate Cyclase ◽  
G Protein ◽  
G Proteins ◽  
Islets Of Langerhans ◽  
Pertussis Toxin ◽  
Inhibitory Receptors ◽  
Rat Islets ◽  
Rat Islets Of Langerhans

Rat islets express a pertussis toxin sensitive G-protein involved in receptor-mediated inhibition of insulin secretion. This has been assumed previously to represent “Gi” which couples inhibitory receptors to adenylate cyclase. Incubation of islet G-proteins with32P-NAD and pertussis toxin resulted in the labelling of a band of molecular weight 40,000. This band was very broad and did not allow resolution of individual components. Incubation of the radiolabelled proteins with an anti-Go antiserum resulted in specific immunoprecipitation of a32P-labelled band. These results demonstrate that the complement of pertussis toxin sensitive G-proteins in rat islets includes Go.

Secretory patterns of 1α-hydroxycorticosterone in the isolated perifused interrenal gland of the dogfish, Scyliorhinus canicula

1990 ◽  
Vol 5 (1) ◽  
pp. 55-60 ◽  
Author(s):  
L. B. O'Toole ◽  
K.J. Armour ◽  
C. Decourt ◽  
N. Hazon ◽  
B. Lahlou ◽  
...  
Keyword(s):  
Angiotensin Ii ◽  
Significant Rise ◽  
Dependent Manner ◽  
Steroid Production ◽  
Secretory Rate ◽  
Scyliorhinus Canicula ◽  
Interrenal Gland ◽  
Dose Dependent ◽  
Stimulation Of

ABSTRACT An isolated in-vitro perifused interrenal gland preparation from the dogfish Scyliorhinus canicula was used to study production of quantitatively the major corticosteroid 1α-hydroxycorticosterone (1α-OH-B), measured by radioimmunoassay. Basal secretory rates were 877·1 ± 145 (s.e.m.) fmol/mg per 15 min (n=14) and the preparation remained viable for up to 22 h, as reflected in a brisk response to 10 μm cyclic AMP (cAMP) after this time. Steroid production responded in a dose-dependent manner to porcine ACTH, with 10 μm producing a maximum stimulation of 225% above the basal secretory rate. cAMP (10 μm) produced an increase of 278% above basal, while 1 μm forskolin increased basal secretory rates by 127%. [Val5]- and [Ile5]-angiotensin II (0·1 μm) increased 1α-OH-B production by 120 and 372% respectively over basal secretory rates. Increasing the concentration of K+ in the perfusate from 8 mm to 12, 18, 28 and 40 mm produced a significant rise only at 28 mm. Alterations in the concentration of Na+ and osmolarity of the perifusion medium had inconsistent effects on steroid production. Increased concentrations of urea (from 360 to 720 mm) increased the basal secretory rate by 121%, whilst reducing the concentration of urea (from 360 to 90 mm) had no effect.

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