Selective α2-adrenoceptor activation by clonidine: effects on 45Ca2 efflux and insulin secretion from isolated rat islets

A possible role for Ca²⁺ in the α-adrenoceptor-induced inhibition of glucose-stimulated insulin secretion was studied in isolated rat islets by the use of the selective α₂-adrenoceptor agonist clonidine. We found that clonidine, in contrast to the a,-adrenoceptor agonist phenylephrine, inhibited glucose-stimulated insulin secretion at dose levels below 10^-6 mol l^-1. In islets preloaded with ⁴⁶Ca²⁺ and perifused at 2 mmol l ^l Ca²⁺, clonidine (10^-6 moll^-1) reduced the glucose (13.3 mmol l^-1)-stimulated ⁴⁶Ca²⁺efflux during both the first and second phases of insulin secretion. Furthermore, the inhibitory effect of clonidine on glucose (13.3 mmol l^-1)-stimulated insulin secretion was partially counteracted by raising the extracellular Ca²⁺ concentrations. Moreover, the calcium channel agonist Bay K 8644 counteracted the inhibition by clonidine on glucose-stimulated insulin secretion. Our results suggest that selective α₂-adrenoceptor-induced inhibition of glucose-stimulated insulin secretion is mediated, at least partially, by restraint of Ca²⁺-influx. This action might in turn be exerted through interference with the voltage-dependent calcium channels.     

Effects of alpha- and beta-adrenoceptor stimulation on 45Ca2+ efflux and insulin secretion from perfused rat islets

Exposure to the beta 2-adrenoceptor agonist terbutaline resulted in a transient stimulation of 45Ca2+ efflux from 45Ca2+ preloaded rat islets perfused in 2 mM Ca2+ and 8.3 mM glucose. Concomitantly, an increase in insulin secretion occurred. Under the same experimental conditions, the alpha-adrenoceptor agonist noradrenaline promptly inhibited insulin release without any apparent influence on 45Ca2+ efflux. In contrast, in a medium containing 2 mM Ca2+ and a low glucose concentration (2.8 mM), terbutaline stimulated insulin secretion without any apparent effects on 45Ca2+ efflux. Noradrenaline had no effect on insulin secretion or 45Ca2+ efflux in this medium. When islets were perfused with 8.3 mM glucose in a Ca2+ deficient medium, with or without addition of the chelating agent EGTA, terbutaline induced a marginal stimulation of insulin secretion and a negligible stimulation of 45Ca2+ efflux. On the contrary, noradrenaline stimulated to an immediate and notable 45Ca2+ efflux in these Ca2+ deficient media. Noradrenaline also clearly inhibited insulin secretion, though less markedly and with a slower onset than in islets perfused in 2 mM Ca2+. When the islets were perfused in a Ca2+ deficient medium with 2.8 mM glucose, terbutaline had a slight insulin releasing effect, but stimulated 45Ca2+ efflux potently. Noradrenaline had no influence on insulin secretion but a weak stimulatory effect on 45Ca2+ efflux. The data suggest that the beta 2-adrenoceptor agonist terbutaline has the ability to stimulate insulin secretion in perfused rat islets, requiring extracellular Ca2+ for the full expression of its effects. These effects may be exerted through a Ca2+-Ca2+ exchange over the cell membrane and/or through cAMP and intracellular Ca2+ perturbations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of α- and β-adrenoceptor stimulation on 45Ca2+ efflux and insulin secretion from perfused rat islets

Exposure to the β₂-adrenoceptor agonist terbutaline resulted in a transient stimulation of ⁴⁵Ca²⁺ efflux from ⁴⁵Ca²⁺ preloaded rat islets perfused in 2 mm Ca²⁺ and 8.3 mm glucose. Concomitantly, an increase in insulin secretion occurred. Under the same experimental conditions, the α-adrenoceptor agonist noradrenaline promptly inhibited insulin release without any apparent influence on ⁴⁵Ca²⁺ efflux. In contrast, in a medium containing 2 mm Ca²⁺ and a low glucose concentration (2.8 mm), terbutaline stimulated insulin secretion without any apparent effects on ⁴⁵Ca²⁺ efflux. Noradrenaline had no effect on insulin secretion or ⁴⁵Ca²⁺ efflux in this medium. When islets were perfused with 8.3 mm glucose in a Ca²⁺ deficient medium, with or without addition of the chelating agent EGTA, terbutaline induced a marginal stimulation of insulin secretion and a negligible stimulation of ⁴⁵Ca²⁺ efflux. On the contrary, noradrenaline stimulated to an immediate and notable ⁴⁵Ca²⁺ efflux in these Ca²⁺ deficient media. Noradrenaline also clearly inhibited insulin secretion, though less markedly and with a slower onset than in islets perfused in 2 mm Ca²⁺. When the islets were perfused in a Ca²⁺ deficient medium with 2.8 mm glucose, terbutaline had a slight insulin releasing effect, but stimulated ⁴⁵Ca²⁺ efflux potently. Noradrenaline had no influence on insulin secretion but a weak stimulatory effect on ⁴⁵Ca²⁺ efflux. The data suggest that the β₂-adrenoceptor agonist terbutaline has the ability to stimulate insulin secretion in perfused rat islets, requiring extracellular Ca²⁺ for the full expression of its effects. These effects may be exerted through a Ca²⁺-Ca²⁺ exchange over the cell membrane and/or through cAMP and intracellular Ca²⁺ perturbations. Moreover, terbutaline directly stimulates ⁴⁵Ca²⁺ efflux, an effect inhibited by glucose. Further, the α-adrenoceptor agonist noradrenaline can inhibit insulin secretion in the absence of extracellular Ca²⁺, but the full expression of its inhibitory action is dependent on extracellular Ca²⁺ and glucose. In addition, noradrenaline stimulates ⁴⁵Ca²⁺ efflux in a Ca²⁺ deficient medium, an effect which appears independent of the glucose concentration.     

Epinephrine modifications of insulin release and of 86Rb+ or 45Ca2+ fluxes in rat islets

The effects of epinephrine on insulin release, 86Rb+ fluxes, and 45Ca2+ fluxes were measured in rat islets. In the presence of 10 mM glucose, epinephrine did not affect 86Rb+ influx and slightly increased net uptake. It caused a monophasic inhibition of release and a biphasic decrease in 86Rb+ efflux. A maximum effect was observed with 1 microM epinephrine, but release was more markedly inhibited by lower concentrations of the catecholamine than was the efflux. Epinephrine inhibition of release and efflux was reversed by phentolamine and yohimbine but not by prazosin or propranolol. It was mimicked by norepinephrine and clonidine. The inhibition of 86Rb+ efflux persisted when insulin release was prevented by omission of extracellular calcium. Ouabain or high K+ markedly increased 86Rb+ efflux in the presence of glucose and epinephrine; theophylline and quinine had a similar but smaller effect. None of these agents restored insulin release. Epinephrine abolished the insulinotropic effect of arginine without altering the rise in 86Rb+ efflux triggered by the amino acid. Epinephrine abolished insulin release but inhibited 45Ca2+ efflux only partially during stimulation by glucose or by barium plus theophylline. The results show that epinephrine does not inhibit insulin release by activating the Na pump or by increasing K permeability of the B cell membrane. On the contrary, the inhibition of release is accompanied by a decrease in 86Rb+ efflux. Both result from activation of alpha 2-receptors but are not causally related; they could be due to remodeling of Ca2+ fluxes and/or changes in cAMP levels.     

Modulation by D-glucose anomers of the effect of D-fructose upon 45Ca efflux from prelabelled rat pancreatic islets

It was recently reported that alpha-D-glucose is more potent than beta-D-glucose in conferring to glucokinase positive cooperativity towards D-fructose. We have now extended pilot experiments to investigate whether a comparable situation prevails in intact rat pancreatic islets in terms of the modulation by the D-glucose anomers of the effect of D-fructose upon 45Ca efflux from prelabelled perifused islets. As expected from the effect of increasing concentrations of equilibrated D-glucose upon 45Ca efflux from the prelabelled islets, D-fructose either decreased or increased 45Ca outflow from islets perifused in the presence of either alpha- or beta-D-glucose. In all cases, the alpha-anomer of D-glucose affected more markedly than beta-D-glucose the cationic response to D-fructose. These findings indicate that the anomeric specificity of the effect of D-glucose upon D-fructose phosphorylation by glucokinase is also operative in intact islets.     

Stimulation of 45Ca2+ efflux from rat pituitary by luteinizing hormone-releasing hormone and other pituitary stimulants.

1. Rat anterior pituitaries were incubated in medium containing 45Ca2+, superfused with non-radioactive medium and the efflux of 45Ca2+ studied. 2. When pituitaries from overiectomized rats were used the addition of LH-RH to the medium at a time when slow exponential efflux of Ca2+ was occurring produced a transient increase in 45Ca2+ efflux simultaneous with or before an increased release of LH. The stimulation of both 45Ca2+ efflux and LH release showed a similar concentration dependence on LH-RH. 3. Increasing the K+ concentration of the medium tenfold also stimulated 45Ca2+ efflux and LH release. The response to LH-RH of both parameters was reduced by superfusion with calcium-free medium. 4. LH-RH induced only a small increase in pituitary 45Ca2+ efflux when intact or thyroidectomized male rats were used. TRH increased 45Ca2+ efflux from thyroidectomized rat pituitaries but had only a small effect when pituitaries from intact or ovariectomized rats were studied. 5. Pretreatment of ovariectomized rats with oestradiol inhibited the subsequent increase in 45Ca2+ efflux induced by LH-RH. 6. It is concluded that the secretagogue induced increase in 45Ca2+ efflux results from an increase in cellular Ca2+ activity which is presumably active in stimulus-secretion coupling.     

Effects of Ca2+ channel agonist-antagonist enantiomers of dihydropyridine 202791 on insulin release, 45Ca uptake and electrical activity in isolated pancreatic islets

This is the first study using the selective agonist/antagonist stereoisomers of dihydropyridine 202791 to investigate stimulus-secretion coupling in pancreatic islet cells. We studied effects of the (+)(Ca2+ channel agonist) and (-)(Ca2+ channel antagonist) forms of the dihydropyridine, on 45calcium net uptake, insulin secretion, and membrane potential measured in rodent islets. The antagonist partially inhibited glucose-induced insulin secretion and Ca2+ uptake; however, the potassium-induced Ca2+ uptake was completely inhibited. The antagonist did not completely block glucose-evoked spike activity. Addition of the agonist enhanced insulin release and Ca2+ uptake in the presence of 5.6 mM-glucose, but did not increase insulin release or Ca2+ uptake in 16.7 mM-glucose. In the presence of tetraethylammonium (TEA), (+)202791 increased and (-)202791 decreased the duration of glucose-induced action potentials. The results again confirm the presence of a dihydropyridine-sensitive Ca2+ channel in pancreatic B-cells. In addition these data suggest that in these cells there is activation of a dihydropyridine-insensitive Ca2+ entry in the presence of glucose.     

Effects of Na+, K+ and Mg2+ on45Ca2+ uptake by pancreatic islets

Microdissected pancreatic islets of noninbredob/ob-mice were used to study ionic effects on the lanthanum-nondisplaceable⁴⁵Ca²⁺ uptake by islet cells. Omission of Mg²⁺ from the incubation medium had no effect, but the⁴⁵Ca²⁺ uptake was increased by omission of Na⁺ and decreased by omission of K⁺. Excess Mg²⁺ (1.2–15 mM) inhibited and excess K⁺ (4.7–25 mM) stimulated the⁴⁵Ca²⁺ uptake in a concentration-dependent manner. Stimulation of⁴⁵Ca²⁺ uptake in Na⁺-deficient islets was associated with an enhancement of the basal insulin release. Total abolishment of glucose-stimulated⁴⁵Ca²⁺ uptake in K⁺-deficient islets did not preclude a significant secretory response to glucose. It is concluded that the lanthanum-nondisplaceable⁴⁵Ca²⁺ uptake shows a partial correlation to insulin release.     

A role of thyrotropin-releasing hormone in insulin secretion by isolated rat pancreatic islets

Insulin-secreting pancreatic cells also express thyrotropin-releasing hormone (TRH). Although the physiological role of TRH in this localization is unclear, its participation in glucoregulation has been implied. To test this hypothesis, we blocked the last step of post-translational maturation of the TRH molecule by disulfiram, which is an active inhibitor of peptide -amidation (PAM) within pancreatic islet cells. The treatment of male rats with 200 mg/kg/day of disulfiram during a 5-day period resulted in a low PAM activity, a high insulin content and its basal secretion from pancreatic islets, and the inability to release insulin in response to glucose (16.7 mM) or hypo-osmotic (30%) challenge in vitro. The addition of TRH (1 nM) to the medium during incubation restored the insulin content and both basal and glucose stimulated insulin secretions to control levels. Conclusion: TRH plays an important role in the mechanism of insulin secretion and its response to glucose stimulation.     

Morphologic basis for loss of regulated insulin secretion by isolated rat pancreatic islets

Laboratories engaged in secretory studies of rat pancreatic islets often encounter high baseline insulin secretion with poor secretory response to secretagogues, such as glucose. The specific morphologic abnormalities that accompany this unregulated release have not been described. We isolated islets comparing two approaches. Both used stationary digestion with collagenase. In method I, we distended the biliary duct extracorporeally with collagenase and minced the pancreas after a 28 min digestion (37°C). In method II, we distended the pancreas intracorporeally and digested for 40 min without mincing. Both methods utilized a similar collagenase concentration (2 μg/ml in Hank's balanced salt solution (HBSS)). Both methods yielded over 300 islets/rat. Islets from both methods appeared intact, when viewed under the dissecting microscope. We found that adequate secretion from incubated islets was evoked with method I, i.e., low basal insulin levels at low glucose (3.3 mM), tripling at 11.0 mM glucose, and nearly quadrupling in response to higher glucose (16.7 mM). In contrast, method II was characterized by high basal levels without response to higher glucose. Ultramicroscopic examination of islet B cells in method I revealed normal cytological features, while B cells in method II showed marked degranulation, profiles of swollen endoplasmic reticulum, and swollen mitochondria. Morphometric analysis of B cells confirmed quantitatively a decrease in secretory granule density and mitochondrial enlargement in method II compared to method I. Anatomic changes, largely confined to the B cells of islets may account for functional alterations of responses. Defects cannot be predicted from gross appearance of islets. © 1993 Wiley-Liss, Inc.     

Effects of Ca2+ ions on gastric acid secretion by the rat isolated stomach

The role of Ca²⁺ in the stimulatory action of histamine has been evaluated in the isolated gastric fundus from immature rats, by changing the concentration of calcium ions in the bathing solutions. Lowering Ca²⁺ to 1.2 mM greatly enhanced the secretory response to histamine, while leaving unaffected that to the H₂-receptor agonist, dimaprit. The effect of histamine was competitively antagonized by ranitidine (pA₂=6.78) in normal solutions; conversely in 1.2 mM Ca²⁺, the antagonism by ranitidine became unsurmountable. Basal rates of acid secretion did not change in low Ca²⁺ solutions, whereas they were reduced approximately by 50% in Ca²⁺-free media. Finally, the secretory response to theophylline was significantly lower in low Ca²⁺ solutions in comparison with that in control conditions. From the above results it may be concluded that changes in the concentration of Ca²⁺ ions caused different changes in the secretory response of the rat stomach in the various experimental conditions. The marked enhancement of the response to histamine observed in low Ca²⁺ is unlikely to be connected with H₂-receptors, as suggested by the lack of interference in the response to dimaprit, but it could be related to intracellular mechanisms (H⁺/K⁺-ATPase, carbonic anhydrase activation etc.).     

Different effects of the ionophore A-23187 and D-glucose on 45Ca2+ fluxes in isolated islets of ob/ob-mice

Fluxes of ⁴⁵Ca²⁺ were studied in β-cell rich islets of non-inbred ob/ob-mice, using LaCl₃ to wash out extracellular and superficially bound ⁴⁵Ca²⁺. The ionophore A-23187 (10,μM) increased the ⁴⁵Ca²⁺ uptake in islets both at 3 and 20 mM D-glucose, the effect being more pronounced after 10 min than after 120 min of incubation. In incubations for 120 min, 20 mM D-glucose induced a higher uptake of ⁴⁵Ca²⁺ than did A-23187. The ionophore enhanced the unidirectional efflux of ⁴⁵Ca^a+ from preloaded islets. Pretreatment of islets with 20 mM D-glucose in non-radioactive medium inhibited the subsequent D-glucose-induced ⁴⁵Ca²⁺ uptake. Similar pretreatment with A-23187 increased the subsequent ionophore-induced ⁴⁵Ca²⁺ uptake. The results suggest that A-23187 acts by catalyzing Ca²⁺ fluxes across the β-cell plasma membrane. The different effects of D-glucose and A-23187 on ⁴⁵Ca²⁺ fluxes suggest that the two agents act through different mechanisms in the β-cells.     

Interactions of Ca2+, Mg2+, and Na+ in regulation of insulin release from rat islets

The effects of glucose and ionic modifications on unidirectional Ca2+ efflux and insulin release has been studied. Rat pancreatic islets were isotopically equilibrated with 45Ca2+ for 2 days and then perifused at 10(-8) M Ca2+ to allow for strict interpretation of 45Ca2+ efflux. Under these conditions 16.7 mM glucose inhibited Ca2+ efflux but did not stimulate insulin release. Removal of Mg2+ from the buffer markedly stimulated Ca2+ efflux that was counteracted by glucose. The omission of Na+ decreased basal Ca2+ efflux by 30% at 10(-8) M Ca2+, thus demonstrating the importance of Na-Ca countertransport for Ca2+ extrusion. Like glucose, Na+ omission or the addition of ouabain attenuated Ca2+ efflux stimulated by Mg2+ removal. Glucose may interfere with Na-Ca countertransport because the actions of 16.7 mM glucose and Na+ omission were not additive. At 10(-8) M Ca2+, glucose elicited insulin release only when both 1) loss of cellular calcium was minimized by prior inhibition of Ca2+ efflux (Na+ omission or ouabain), and 2) Ca2+ mobilization was favored by Mg2+ removal. Under these conditions (in contrast to normal Ca2+), insulin release was not accompanied by increased Ca2+ efflux. Thus, unidirectional Ca2+ measurements do not permit the detection of Ca2+ mobilization in intact islets because glucose may concomitantly inhibit Ca2+ extrusion.     

The mechanism of increasing Ca2+ responsiveness by alpha1-adrenoceptor stimulation in rat ventricular myocytes

We investigated the mechanism of alpha(1)-adrenoceptor stimulation on the myofibrillar Ca(2+) responsiveness at steady-state in intact rat ventricular myocytes. We produced tetanus, and an instantaneous plot of [Ca(2+)](i) vs. cell length (Ca-L trajectory) was constructed to estimate the Ca(2+) responsiveness. An alpha(1)-agonist, phenylephrine, dose-dependently shifted the Ca-L trajectory to the left, corresponding to sensitization of the myofilaments. An alpha(1)-antagonist, prazosin, and inhibition of the Na/H exchange by ethylisopropylamiloride (EIPA) completely reversed the phenylephrine-induced shift. Phenylephrine increased pH(i) (DeltapH(i) = +0.1), which was reversed by prazosin and EIPA. Chelerythrine, an inhibitor of protein kinase C (PKC), completely blocked the effects of phenylephrine on Ca(2+) responsiveness and pH(i). When pH(i) was increased (DeltapH(i) = +0.1) without phenylephrine by changing pH(o), the Ca-L trajectory was shifted to the same extent as that observed with phenylephrine. We conclude that alpha(1)-adrenoceptor stimulation activates Na/H exchange through a PKC-mediated pathway and that an increase in pH(i) is mainly responsible for the increase in Ca(2+) responsiveness.     

Effects of CO2, acetylcholine and caerulein on45Ca efflux from isolated mouse pancreatic fragments

Mouse pancreatic fragments were loaded with⁴⁵Ca and placed in a flow cell. The concentration of⁴⁵Ca in the effluent was measured. The effects of changing the tension of carbon dioxide on⁴⁵Ca efflux were observed and compared with effects of pancreatic secretagogues.The normal control solution was equilibrated with 5% CO₂, 95% O₂. Shift to solutions equilibrated with 10, 20, 50 or 100% CO₂ evoked a dose-dependent increase in fractional⁴⁵Ca efflux, with a just detectable effect at 10% and a maximal one at 50%.The CO₂-evoked Ca release was not due to anoxia, since a short period of exposure to a 100% N₂-equilibrated solution had no effect. A decrease in extracellular pH (tris buffering) had only a very modest effect on⁴⁵Ca efflux.CO₂-evoked Ca release under conditions avoiding extracellular pH changes (20% CO₂, 100 mM NaHCO₃). This CO₂-evoked enhanced⁴⁵Ca efflux was sustained during a 30 min stimulation period, but was abruptly terminated on return to the control solution (5% CO₂, 25 mM NaHCO₃). NH₃ (10 mM) added to the 20% CO₂-equilibrated solution for a brief interval in the middle of a period of CO₂-evoked enhanced⁴⁵Ca efflux evoked a rapid return of the fractional Ca efflux towards the resting level. This effect was rapidly reversible.While the CO₂-evoked Ca release was largely sustained, the ACh-evoked increase in⁴⁵Ca fractional efflux was entirely transient. The CO₂-evoked Ca release was not inhibited by a background of sustained ACh stimulation. ACh-evoked Ca release, however, was markedly inhibited in the presence of sustained CO₂ stimulation.2,4 Dinitrophenol (1 mM) in combination with iodoacetate (2 mM), while markedly reducing⁴⁵Ca uptake into the fragments during the loading period had little or no effect on the ACh-evoked increase in⁴⁵Ca fractional efflux. The CO₂-evoked Ca release, however, was markedly reduced by these metabolic inhibitors.The local anaesthetic procaine (1 mM) virtually abolished ACh- or caerulein-evoked Ca release without having any influence on the CO₂ effect.It is concluded that CO₂ releases Ca from pancreatic acinar cells by means of intracellular acidification. This effect may in part be due to H⁺ displacement of Ca²⁺ from intracellular membrane binding sites and partly due to release of Ca from compartments (organelles) into which Ca has been actively accumulated.     

Different effects of the ionophore A-23187 and D-glucose on 45Ca2+ fluxes in isolated islets of ob/ob-mice.

Fluxes of 45Ca2+ were studied in beta-cell rich islets of non-inbred ob/ob-mice, using LaCl3 to wash out extra-cellular and superficially bound 45Ca2+. The ionophore A-23187 (10 microM) increased the 45Ca2+ uptake in islets both at 3 and 20 mM D-glucose, the effect being more pronounced after 10 min than after 120 min of incubation. In incubations for 120 min, 20 mM D-glucose induced a higher uptake of 45Ca2+ than did A-23187. The ionophore enhanced the unidirectional efflux of 45Ca2+ from preloaded islets. Pretreatment of islets with 20 mM D-glucose in non-radioactive medium inhibited the subsequent D-glucose-induced 45Ca2+ uptake. Similar pretreatment with A-23187 increased the subsequent ionophore-induced 45Ca2+ uptake. The results suggest that A-23187 acts by catalyzing Ca2+ fluxes across the beta-cell plasma membrane. The different effects of D-glucose and A-23187 on 45Ca2+ fluxes suggest that the two agents act through different mechanisms in the beta-cells.     

Ghrelin促进大鼠胰岛素合成及高葡萄糖诱导的胰岛素分泌

Ghrelin是由胃黏膜分泌的小分子脑肠肽。本研究探讨了Ghrelin对于大鼠胰岛细胞合成与分泌胰岛素的影响。将分离培养的大鼠胰岛分为Ghrelin处理组和对照组 :(1)在高浓度葡萄糖 (16 7mmol L)刺激时加入不同浓度Ghrelin 10 - 1 2 ～ 10 - 8mol L孵育 6 0min ,测定胰岛素分泌量。 (2 )在培养液中加入不同浓度Ghrelin 10 - 1 2 ～ 10 - 8mol L预处理 2 4h后 ,用RT PCR方法检测胰岛内前胰岛素原mRNA表达 ,并测定不同浓度葡萄糖 (5 6mmol L ,16 7mmol L)刺激时胰岛素分泌量。离体大鼠胰岛 ,在高糖刺激时加入Ghrelin 10 - 1 1 ～ 10 - 1 0 mol L共同培养 6 0min ,胰岛素分泌量增加高于对照组 (P <0 0 5 )。Ghrelin 10 - 1 2 ～ 10 - 1 0 mol L预处理 2 4h后 ,高糖刺激时胰岛素分泌量增加高于对照组 (P <0 0 5 ) ,同时Ghrelin 10 - 1 0 mol L促进胰岛内前胰岛素原mRNA表达高于对照组 (P <0 0 5 )。一定浓度的Ghrelin促进胰岛在高葡萄糖诱导下的胰岛素分泌 ,经Ghrelin预处理 2 4h后该作用更为显著。Ghrelin增加大鼠胰岛内前胰岛素原mRNA的表达 ,促进胰岛素合成。     

Different effects of glibenclamide and the structural analogue HB 699 on the 45Ca2+ uptake by ob/ob-mouse islets

The effects on 45Ca2+ uptake of HB 699, an acyl-amino-alkyl benzoic acid derivative, was compared to those of glibenclamide in incubations using the La3+ wash technique. HB 699 enhanced the 45Ca2+ net uptake in a concentration range (10-200 microM) where insulin release was also stimulated. Glibenclamide showed maximum stimulation of 45Ca2+ net uptake already at 1 microM. HB 699 did not clearly stimulate the short-term 45Ca2+ uptake whether or not the islets were preincubated with the drug. It is suggested that HB 699-induced insulin release is mediated, at least partly, by increased mobility of beta-cell Ca2+.