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G Skoglund

Publications and source records attributed to G Skoglund.

36 records · Page 2Linked to original sources
PubMed1989

Insulin secretion and islet lysosomal enzyme activities in the mouse. Effects of suramin.

To study the functional role of the lysosomes in islet physiology, we have in the present study investigated influences on insulin secretion induced by a primary inhibition of islet lysosomal enzyme activities by the use of the lysosomotropic drug suramin. First, we demonstrated that the activities of the three lysosomal enzymes, acid amyloglucosidase, acid alpha-glucosidase, and N-acetyl-beta-D-glucosaminidase, were inhibited in mouse islet homogenates upon direct addition of suramin (p less than 0.001). Thereafter, we studied the influences of suramin on islet lysosomal enzyme activities at 24 h after an administration of suramin to mice. We thereby found that the islet lysosomal enzyme activities were not significantly altered compared to controls. However, after incubation of the islets at 3.3 mM glucose, the activities of acid amyloglucosidase and acid alpha-glucosidase were increased (p less than 0.05). The activity of N-acetyl-beta-D-glucosaminidase was, however, not affected. Hence, the direct inhibitory action on islet lysosomal enzyme activities by suramin seems to be counteracted in vivo. Concurrently with the increased enzyme activities in incubated islets, glucose-induced insulin secretion was significantly potentiated by suramin pretreatment (p less than 0.01). In contrast, suramin pretreatment did impair the glucose-induced insulin secretion in vivo (p less than 0.01). The direct effects on plasma insulin and glucose levels of acutely administered suramin were also studied. It was found that at a high dose level, suramin slightly reduced the basal plasma insulin levels (p less than 0.05). Suramin did not, however, affect the glucose-induced increase in plasma insulin levels. Conversely, at a low dose level, suramin potentiated glucose-induced increase in plasma insulin levels (p less than 0.01). A similar potentiated glucose-induced insulin secretion by suramin was also observed by a direct addition of the drug to islets in vitro. In conclusion, this study demonstrates that suramin inhibits lysosomal enzyme activities in islet homogenates, increases the activity of acid amyloglucosidase and acid alpha-glucosidase in incubated mouse islets after administration of the drug in vivo and potentiates glucose-stimulated insulin secretion from islets in vitro after administration of the drug in vivo. Thus, we suggest first, that in vivo, compensatory mechanisms may counteract the direct inhibitory influence of suramin on islet lysosomal enzyme activities, and second, that in vitro, islet lysosomal acid amyloglucosidase and acid alpha-glucosidase activities and glucose-induced insulin secretion are regulated in parallel.

Acetylglucosaminidase↗
PubMed1989

Insulin secretion in neonatally streptozotocin-injected mice.

Streptozotocin (150 mg/kg) was given intraperitoneally at the age of two and three days to neonatal mice. At three weeks of age, these streptozotocin-treated mice were hyperinsulinemic but normoglycemic when compared to controls indicating a relative inhibition of insulin action. From the age of five weeks, the streptozotocin-treated mice were hyperglycemic. The diabetes prevalence in streptozotocin-treated mice started to increase between three and five weeks of age, to finally become approximately 25%. At five weeks of age, the plasma insulin response to glucose was still normal in streptozotocin-treated mice, whereas carbachol-induced insulin secretion was impaired with no difference between those with and those without diabetes. At 10 weeks of age, all diabetics had impaired glucose- and carbachol-induced increase in plasma insulin levels, whereas streptozotocin-treated mice without diabetes had plasma insulin responses within the normal range. This study shows that intraperitoneal injection of streptozotocin to neonatal mice results in a permanent diabetes prevalence of approximately 25%. The study also suggests that during the progression to diabetes in streptozotocin-injected neonatal mice, impairment of glucose-stimulated insulin secretion occurs but this impairment is initially compensated. In contrast, a defect in carbachol-stimulated insulin secretion is not compensated and therefore visible earlier.

Aging↗
PubMed1988

H2O2 activates CD11b/CD18-dependent cell adhesion.

Treatment of monoblastoid U-937 cells with low concentrations of H2O2 caused adhesion of the cells to plastic. The H2O2 induced adhesion was rapid with a t1/2 of congruent to 6 min and was optimally stimulated by 100 microM H2O2 with an ED50 of congruent to 50 microM. The response to H2O2 closely resembled the adhesive response of U-937 cells to phorbol esters in its time dependency, requirement for extracellular Mg2+ and inhibition by cytochalasin B as well as inhibition by monoclonal antibodies against the leucocyte adhesion molecules CD11b and CD18. Phorbol ester treatment of U-937 cells stimulated the phosphorylation of at least three endogenous substrates, pp28, pp34 and pp43, of which pp28 and pp43 also responded to H2O2-treatment with increased 32P-incorporation. The results suggest that H2O2 might be a physiological modulator of leucocyte adhesion, possibly operating by activating protein kinase C.

Antibodies, Monoclonal↗
PubMed1988

Phorbol-ester-induced stable changes in the regulation of DNA synthesis and intracellular pH are accompanied by altered expression of protein kinase C in the monoblastoid cell line U-937.

12-O-tetradecanoylphorbol-13-acetate (TPA)-induced changes in cytoplasmic pH, cytoplasmic Ca2+-concentration, rate of DNA synthesis, and concentration and activity of protein kinase C (PKC) were studied in human monoblastoid cell lines. The cell line U-937 GTB was compared to the subline U-937 RES (adapted to growth in the presence of 10(-9) M TPA) and another subline U-937 RESREV (U-937 RES grown in TPA-free medium) established in order to analyze the stability of the TPA-induced differences. TPA induced half maximal inhibition of DNA synthesis in the wild-type U-937 GTB cell line at 10(-9) M, whereas 10 times higher concentrations of phorbol ester were needed for a corresponding inhibition of the U-937 RES and U-937 RESREV lines. Furthermore, the U-937 RES cells exhibited a decreased sensitivity to TPA, and the U-937 RESREV cells did not respond at all to this agent with regard to cytoplasmic alkalinization by an intracellular mechanism independent of Na+/H+ exchange. A Na+-dependent system for extrusion of protons, which was activated by the Ca2+ ionophore ionomycin, was also severely depressed as a result of TPA-adaptation. The concentration of PKC, measured by immunoblotting, was reduced by 34 and 24% in U-937 RES and U-937 RESREV cells, respectively, as compared to the wild-type U-937 GTB line. The corresponding reductions in PKC activity were 32 and 54% when histone III-S was used as substrate. The data suggest that adaptation to growth in the presence of TPA results in stable modifications of several parameters, which are assumed to be involved in the regulation of proliferation and differentiation. Furthermore, the data from the U-937 RESREV cells question a causal relationship between cytoplasmic alkalinization and control of proliferation.

Cell Line↗
PubMed1988

Evidence for separate control by phorbol esters of CD18-dependent adhesion and translocation of protein kinase C in U-937 cells.

Treatment of U-937 GTB cells with tumor-promoting phorbol esters induced adherence of the cells to plastic, with a t1/2 of 20 min. The ED50 was determined to 3.3 nM for phorbol-12,13-dibutyrate and 0.3 nM for 12-O-tetradecanoyl-4 beta-phorbol-13-acetate, whereas the non-tumor-promoting analogue 12-O-tetradecanoyl-4 alpha-phorbol-13-acetate was ineffective at concentrations up to 100 nM. The adherence process showed characteristics typical of leucocyte adhesion and was inhibited by a monoclonal antibody to the leucocyte adhesion molecule CD18. The sublines of U-937, RES and RESREV made resistant to the action of low doses of phorbol ester regarding inhibition of DNA synthesis and containing lower levels of protein kinase C compared to U-937 GTB, were desensitized with respect to the adhesion response. Translocation of protein kinase C from cytosol to the particulate fraction occurred at about 10-fold higher concentrations of phorbol ester than the adhesion response in U-937 GTB cells, under otherwise similar conditions, whereas no difference in sensitivity was observed between the sublines. Also phorbol ester stimulation of choline incorporation into lipids exhibited lower sensitivity compared to the adhesion response with no difference observed between the various cell lines. The results indicate that CD18-dependent adhesion, like DNA synthesis, is controlled by phorbol esters in a manner unrelated to the translocation of protein kinase C and that the control mechanism might involve forms of protein kinase C which are subject to stable down-modulation following TPA adaption of the cells.

Cell Adhesion↗
PubMed1988

Protein kinase C-dependent phosphorylation of profilin is specifically stimulated by phosphatidylinositol bisphosphate (PIP2).

Calf spleen profilin is shown to be an in vitro substrate of purified human placental protein kinase C (PKC), with an apparent Km of 4 microM. Phosphatidylinositol bisphosphate (PIP2) was an effective activator of the profilin phosphorylation by PKC and caused a maximum 13-fold increase of Vmax with a half maximal effect at 40 micrograms/ml. The action of PIP2 was not mimicked by phosphatidylserine, phosphatidic acid or phosphatidylinositol, whereas phosphatidylinositol monophosphate was slightly stimulatory. By contrast, protein kinase C-dependent phosphorylation of histone type III-S, myelin basic protein or lipocortin-I was not affected by PIP. It is suggested that PIP2 modifies the nature of the profilin-PKC interactions.

Amino Acids↗
PubMed1988

Selective alpha 2-adrenoceptor activation by clonidine: effects on 45Ca2+ efflux and insulin secretion from isolated rat islets.

A possible role for Ca2+ in the alpha-adrenoceptor-induced inhibition of glucose-stimulated insulin secretion was studied in isolated rat islets by the use of the selective alpha 2-adrenoceptor agonist clonidine. We found that clonidine, in contrast to the alpha 1-adrenoceptor agonist phenylephrine, inhibited glucose-stimulated insulin secretion at dose levels below 10(-6) mol l-1. In islets preloaded with 45Ca2+ and perifused at 2 mmol l-1 Ca2+, clonidine (10(-6) mol l-1) reduced the glucose (13.3 mmol l-1)-stimulated 45Ca2+ 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 alpha 2-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.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1988

Islet hormone secretion and islet lysosomal enzyme activities in the mouse: effects of chloroquine.

To examine the function of islet lysosomal enzymes in islet hormone secretory mechanisms, we investigated the effects of the lysosomotropic drug chloroquine on islet lysosomal enzyme activities and basal as well as stimulated insulin and glucagon secretion. Chloroquine, added to islet homogenates, did not affect the activities of the lysosomal enzymes acid amyloglucosidase, acid alpha-glucosidase, or N-acetyl-beta-D-glucosaminidase. The activity of acid phosphatase, however, was inhibited at a high concentration of chloroquine (10(-3) M). When injected together with glucose, chloroquine (2 or 10 mumol/kg) inhibited the peak plasma insulin response. Similarly, at 24 hrs after chloroquine injection (100 mumol/kg), the plasma insulin response to glucose was reduced. In contrast, islets isolated from mice pretreated 24 hrs before with chloroquine, displayed glucose-stimulated insulin secretion in vitro that was not different from controls. Such islets showed, furthermore, enhanced activities of the enzymes acid phosphatase and neutral alpha-glucosidase but not of acid amyloglucosidase, acid alpha-glucosidase or N-acetyl-beta-D-glucosaminidase. Arginine-stimulated insulin response in vivo displayed a complex pattern; it was increased when arginine was injected together with chloroquine but decreased at 24 hrs after chloroquine administration. Arginine-stimulated glucagon secretion was not affected by chloroquine. We conclude that chloroquine pretreatment 24 hrs prior to glucose injection decreases glucose-stimulated insulin secretion in vivo by mechanisms that are not correlated to an inhibitory action on islet activities of glycogenolytic lysosomal enzymes.

Animals↗
PubMed1987

Alpha 1- and alpha 2-adrenoceptor activation increases plasma glucagon levels in the mouse.

The effects of activation of the alpha-adrenoceptors on glucagon secretion are not yet clear. We therefore injected the alpha 1-selective agonist phenylephrine and the alpha 2-selective agonist clonidine (0.05-50 nmol/kg) intravenously to mice and measured the plasma glucagon levels. We found that both phenylephrine and clonidine enhanced the plasma glucagon levels. The peak level of plasma glucagon was seen at 2 min after clonidine injection whereas phenylephrine enhanced the plasma glucagon levels throughout a 10 min period after the injection. Furthermore, both clonidine and phenylephrine potentiated the plasma glucagon response to the cholinergic agonist carbachol and exerted additive stimulatory effects on the plasma glucagon response to both the beta-adrenoceptor agonist terbutaline and the C-terminal octapeptide of cholecystokinin, CCK-8. The elevated plasma insulin levels after injection of carbachol or terbutaline were lowered by clonidine but not by phenylephrine whereas the CCK-8-induced increase in plasma insulin levels was not affected by either clonidine or phenylephrine. We conclude that both alpha 1- and alpha 2-adrenoceptor activation enhances plasma glucagon levels in the mouse, and that alpha 2- but not alpha 1-adrenoceptor activation lowers plasma insulin levels.

Adrenergic alpha-Agonists↗
PubMed1987

Glycogen and glycogen-hydrolysing lysosomal enzyme activity in mouse liver: effects of fasting, adrenoceptor antagonism and insulin-induced hypoglycaemia.

Whereas the phosphorolytic breakdown of liver glycogen is known to be of great physiological importance, the functional role of the hydrolytic glycogenolysis in the lysosomal system is less well understood. In the present study the effects of fasting, alpha- and beta-adrenoceptor antagonism and insulin-induced hypoglycaemia on liver lysosomal glycogen-hydrolysing enzyme activity were investigated in mice. In freely fed mice the glycogen-hydrolysing activity (acid amyloglucosidase) was only 50% of the maltose-hydrolysing activity (acid maltase). Starvation for 24 h reduced the acid amyloglucosidase activity by approximately 30% (P less than 0.001), whereas the activities of acid maltase, acid phosphatase and beta-glucuronidase appeared unaffected. N-acetyl-beta-D-glucosaminidase activity was moderately (20%; P less than 0.01) enhanced by fasting. Thus, liver lysosomal enzyme activities may change independently of each other during fasting. Further, during short-term hypoglycaemic conditions (45 min) induced by endogenous or exogenous insulin, the activity of liver acid amyloglucosidase was found to be moderately reduced (15-20%). Blockade of alpha- and beta-adrenoceptors by phentolamine and propranolol did not result in any apparent influence on acid amyloglucosidase activity except for the indirect effect exerted by the phentolamine-induced hypoglycaemia. A moderate negative correlation (r = -0.51; P less than 0.001) between total liver glycogen concentration and acid amyloglucosidase activity was observed in a series of 43 freely fed NMRI mice. Our data show that in mouse liver the acid maltase activity predominates over the acid amyloglucosidase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1987

Biochemical determination of islet lysosomal enzyme activities following crinophagy-stimulating treatment with diazoxide in mice.

The pattern of islet lysosomal enzyme activities, islet insulin concentration and the plasma levels of insulin and glucose were studied in freely fed mice after the in vivo administration of diazoxide in doses known to induce crinophagy in islet beta-cells. After diazoxide treatment at time 0 and at 18 hr, the plasma glucose levels at 20 hr were markedly enhanced from 6.6 +/- 0.2 mmol/l (controls) to 27.2 +/- 2.7 mmol/l (diazoxide). Inhibition of insulin secretion by diazoxide was reflected in the insulinogenic index, which was reduced by approximately 40% (p less than 0.01) in the diazoxide-treated animals, who also displayed an increased concentration of islet insulin (+50%; p less than 0.01). Moreover, we found that the activities of certain lysosomal enzymes in islet tissue were markedly increased following diazoxide treatment. Thus the activities of the acid phosphatase, (+57%; p less than 0.02) the hexosaminidase N-acetyl-beta-D-glucosaminidase, (+52%; p less than 0.001), and the carboxyl proteinase cathepsin D (+41%; p less than 0.001), were all enhanced after diazoxide, whereas the activity of another lysosomal enzyme, the glycogen hydrolysing acid amyloglucosidase, was not altered by diazoxide treatment. The present data thus indicate that the morphological observation of diazoxide-induced crinophagy in pancreatic beta-cells has a biochemical correlate in enhanced levels of certain islet lysosomal enzyme activities known to participate in degradative processes. The results also suggest that islet lysosomal enzyme activities and/or lysosome populations can be modulated by a relative independence from each other.

Acetylglucosaminidase↗
PubMed1986

Effects of alpha 1- and alpha 2-adrenoceptor stimulation and blockade on plasma insulin levels in the mouse.

Stimulation of alpha-adrenoceptors is known to inhibit insulin secretion under a variety of conditions. In this study, the question of whether these alpha-adrenoceptors are of the alpha 1- or the alpha 2-subtype was investigated in the mouse. The selective alpha 2-adrenoceptor agonist clonidine (0.05-50 nmol/kg) was found to markedly inhibit the insulin secretory response to both glucose and the cholinergic agonist carbachol. This inhibition of insulin secretion was counteracted by the alpha 2-adrenoceptor antagonist yohimbine (2.6 mumol/kg), but not by the alpha 1-adrenoceptor antagonist prazosin (2.6 mumol/kg). In contrast, the alpha 1-adrenoceptor agonist phenylephrine (0.05-50 nmol/kg) did not affect the insulin secretory response to either glucose or carbachol. Moreover, both yohimbine and prazosin increased basal plasma insulin levels. It is concluded that alpha 1- and alpha 2-adrenoceptor blockade is followed by enhancement of basal plasma insulin levels in the mouse, whereas alpha 2-adrenoceptor stimulation but not alpha 1-adrenoceptor stimulation impairs the insulin secretory response to glucose and carbachol.

Adrenergic alpha-Agonists↗
PubMed1986

Increased insulin secretion in response to glucose in isolated islets of Langerhans from bile duct-occluded rats.

In a recent study, it was demonstrated that following i.v. injection of glucose, plasma insulin levels increased more in cholestatic rats than in control rats. This could theoretically be due to either a potentiated insulin secretion or an inhibited liver extraction of insulin in cholestatic rats. In the present study, we report the influence of obstructive jaundice on insulin secretion from isolated islets of Langerhans 3 weeks after bile duct occlusion or sham operation in rats. We found that insulin secretion from islets of control rats (250 +/- 29 microU/ml) and of bile duct-occluded rats (260 +/- 24 microU/ml) was not significantly different in a medium with a low glucose concentration (3.3 mM). In contrast, at a high glucose level (16.7 mM), an increased insulin secretion was seen from islets of cholestatic rats (469 +/- 14 microU/ml) as compared with control rats (370 +/- 19 microU/ml) (p less than 0.001). These results indicate that the increased plasma insulin levels found in vivo during cholestasis may not merely reflect a decreased liver clearance but be attributed to a potentiation of glucose-induced insulin secretion.

Animals↗
PubMed1986

Insulin secretion and lysosomal enzyme activities in isolated mouse islets. Effects of glucose, diazoxide and isobutylmethylxanthine.

The influences of glucose, the benzothiadiazide derivative diazoxide (an inhibitor of insulin release), and the potent non-glucose insulin secretagogue 3-isobutyl-1-methylxanthine (IBMX) on insulin secretion and the activities of 3 different lysosomal enzymes were studied in isolated mouse islets. We found that the increase in insulin secretion during a 4 hr incubation period in the presence of 16.7 mM glucose was accompanied by an increase in islet activities of the lysosomal enzymes acid amyloglucosidase and acid alpha-glucosidase. These alpha-1,4-glucoside splitting enzyme activities were increased by 45-55% (p less than 0.01). No influence by glucose was encountered for the activities of N-acetyl-beta-D-glucosaminidase or the non-lysosomal neutral alpha-glucosidase. Upon incubation with 0.2 mM diazoxide and glucose (16.7 mM) the glucose-induced insulin secretion was markedly suppressed and no significant increase in islet lysosomal enzyme activities was observed. On the other hand, insulin secretion induced by IBMX to the same magnitude as with 16.7 mM glucose, was accompanied by an increase in islet activity of N-acetyl-beta-D-glucosaminidase (p less than 0.05), whereas no apparent changes in acid amyloglucosidase and acid alpha-glucosidase activities could be detected. In conclusion, the determination of lysosomal enzyme activities in isolated mouse islets revealed that glucose was able to induce an increased activity of glucose producing glycogenolytic acid hydrolases under conditions when a concomitant insulin secretion occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1985

Rapid effects of phorbol esters on isolated rat adipocytes. Relationship to the action of protein kinase C.

Treatment of isolated rat adipocytes with tumor-promoting phorbol esters, caused a fivefold stimulation of glucose oxidation, determined as 14CO2 production from [1-14C]glucose and a fivefold increase in the rate of lipid synthesis from [14C]glucose. Treatment of the cells with 12-O-tetradecanoylphorbol 13-acetate increased the rate of 86Rb+ uptake into the cells. Also phospholipase C was able to stimulate the rate of glucose oxidation; phospholipase C and 12-O-tetradecanoylphorbol 13-acetate stimulated glucose oxidation in a non-synergistic fashion, indicating a common mechanism for their action. Active phorbol esters and, in part, also phospholipase C, caused a translocation of protein kinase C activity from the soluble to the particulate fraction of the adipocytes. This process was rapid, being complete 30 s after the addition of phorbol ester, and resulted in the appearance of the kinase mainly in the mitochondrial and plasma membrane fractions. A comparison between the binding characteristics of adipocyte protein kinase C and the metabolic effects of the phorbol esters on the adipocytes revealed that the dose-response relationship did not correlate with binding of the phorbol esters, but, rather, a correlation was observed between the dose of phorbol esters required for translocation of protein kinase C and the intracellular effects. The results indicate that the intracellular translocation of protein kinase C might be a trigger for the effects of phorbol esters on the adipocyte and that binding of the esters to protein kinase C is not a sufficient event to cause this effect. Furthermore, it is suggested that activation of protein kinase C might be partly the action of hormones, such as insulin, on the fat cells.

Adipose Tissue↗
PubMed1985

Characterization of calcium and phospholipid dependent protein kinase in isolated rat adipocytes.

Calcium and phospholipid-dependent protein kinase (protein kinase C) from isolated rat adipocytes has been partially purified using DEAE-Sepharose CL-6B and characterized. The enzyme was shown to have similar properties as the kinase isolated from brain or spleen. When histone was used as substrate, an equal amount of cAMP-dependent and calcium and phospholipid-dependent kinase activity was detected from the DEAE Sepharose CL-6B fractions. The major part of protein kinase C (72%) was isolated from the soluble adipocyte fraction. Of the membranous fractions, the plasma membrane exhibited the highest specific activity. The protein kinase preparations bound [3H]-phorbol-12,13-dibutyrate (PDBU) with high affinity (Kd = 2 nM) and the number of PDBU binding sites per cell was calculated to 63 000.

Adipose Tissue↗
PubMed1985

Phorbol ester-induced alteration of differentiation and proliferation in human hematopoietic tumor cell lines: relationship to the presence and subcellular distribution of protein kinase C.

The intracellular translocation of protein kinase C (PKC) from the soluble to the membranous fraction has been shown previously to correlate with biological activity of phorbol esters in several systems. In this paper, we describe that PKC translocation was a general phenomenon in all PKC containing cell types when five 12-O-tetradecanoylphorbol-13-acetate (TPA) responsive and nonresponsive hematopoietic tumor cell lines were investigated. The nonresponsive cell line U-266 contained undetectable levels of PKC. The dose of TPA required for translocation was similar to the TPA concentration necessary to suppress erythroid differentiation in K-562 cells and to induce macrophage differentiation in U-937 cells, but 100-fold higher than that required for suppression of proliferation in K-562 and U-937 cells. By contrast, PKC translocation and TPA induced proliferation inhibition exhibited a similar dose dependence in a subline of U-937 (U-937 RES) adapted to growth in the presence of 10(-9) M TPA. It is suggested that U-937 RES is deficient in a TPA dependent but PKC independent signal pathway.

Biological Transport↗