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S Zeuzem

Publications and source records attributed to S Zeuzem.

At least 199 records · Page 11Linked to original sources
PubMed1993

A synthetic peptide of the effector domain of rab3A stimulates inositol 1,4,5-trisphosphate production in digitonin-permeabilized pancreatic acini.

In this study we report that a synthetic peptide of the effector domain of rab3A (rab3AL(33-48)) stimulates both amylase secretion and inositol 1,4,5-trisphosphate (IP3)-accumulation in digitonin-permeabilized pancreatic acini in an analogous way to cholecystokinin-octapeptide (CCK8). Maximum CCK8-induced IP3-accumulation was observed at five seconds after addition of CCK8 to the acini. Maximum rab3AL(33-48)-induced IP3-production occurred 15 to 30 seconds after addition of rab3AL(33-48); then the acinar IP3 content declined towards the basal level. Heparin, an inhibitor of IP3 binding to its receptor, inhibited both rab3AL(33-48)- and CCK8-stimulated amylase secretion without affecting the response to vasoactive intestinal polypeptide. rab3AL(33-48) had no effect in intact acini, indicating that the site of action of rab3AL(33-48) is intracellular. We conclude that rab-like small molecular weight GTP-binding proteins regulate phospholipase C activity and thereby amylase secretion from inside of the cell.

Amylases↗
PubMed1993

Effect of epidermal growth factor on cholecystokinin-induced amylase release and inositol 1,4,5-trisphosphate production in pancreatic acinar cells.

In the present study we investigated the role of epidermal growth factor (EGF) in cholecystokinin-octapeptide (CCK8)-induced inositol 1,4,5-trisphosphate (IP3) production and amylase release. The data show that high EGF concentrations (90 nM) increased the basal amylase release, but did not increase the acinar IP3 content. High EGF concentrations shifted the dose-response curve for CCK8-induced amylase release to lower CCK8 concentrations, whereas low EGF concentrations (17 nM) shifted this dose-response curve to higher CCK8 concentrations. 17 nM EGF inhibited CCK8-induced IP3 production during the whole period of observation of 5 min, whereas 90 nM EGF inhibited only the initial component (15 s) of CCK8-induced IP3 production. At later time points, 90 nM EGF increased CCK8-induced IP3 production. We conclude that low concentrations of EGF are inhibitory on CCK8-induced IP3 production and amylase release, whereas high EGF concentrations stimulate CCK8-induced amylase release.

Amylases↗
PubMed1993

Effects of guanine nucleotides on bombesin-stimulated signal transduction in rat pancreatic acinar cells.

To study the role of guanine nucleotide binding proteins (G proteins) in bombesin receptor signal transduction, we investigated the effects of guanine nucleotide analogues and of the G protein activator NaF on bombesin-induced amylase release, inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) production and release of intracellular Ca2+ in rat pancreatic acini. In digitonin-permeabilized acini, guanosine 5'-[gamma-thio]triphosphate (GTP gamma S), a well-known activator of G proteins, potentiated bombesin-induced Ins(1,4,5)P3 production and increased amylase release at low bombesin concentrations (< 10 nM). By contrast, GTP gamma S decreased bombesin-stimulated amylase release at high bombesin concentrations (> 10 nM). Fluoride (10 mM), another G protein activator, had similar effects to GTP gamma S on amylase release. However, unlike GTP gamma S it had no effect on Ins(1,4,5)P3 production and release of intracellular Ca2+ induced by high bombesin concentrations. GDP and its analogues, such as 2'-desoxyguanosine 5'-diphosphate (dGDP) or guanosine 5'-[beta-thio]diphosphate (GDP beta S), inhibit activation of G proteins. GDP and dGDP both inhibited amylase release and Ins(1,4,5)P3 production at all bombesin concentrations tested. In contrast, GDP beta S mimicked the effects of GTP gamma S on bombesin-stimulated amylase release and Ins(1,4,5)P3 accumulation. In conclusion, we suggest that bombesin receptor-mediated signal transduction involves G proteins in pancreatic acini. The correlation between inhibition of maximum-stimulated enzyme secretion and further increase in Ins(1,4,5)P3 production in response to GTP gamma S at high bombesin concentrations suggests that overstimulation of phospholipase C inhibits amylase release. The discrepant effects of GDP and of GDP beta S on phospholipase C activity and amylase release might be due to the ability of GDP beta S, but not of GDP to activate G proteins persistently after phosphorylation by G protein-associated GDP kinases.

Amylases↗
PubMed1992

Intravesicular acidification correlates with binding of ADP-ribosylation factor to microsomal membranes.

The ADP-ribosylation factor (ARF), a highly conserved low molecular weight GTP-binding protein, has been implicated to function in intracellular protein transport to and within the Golgi complex. In pancreatic acinar cells the ARF is confined to the cytoplasmic faces of trans-Golgi stack membranes, a compartment known to maintain a low intravesicular pH, which is established by a chloride-dependent MgATP-driven proton pump. The present study shows that MgATP (2mM), but neither adenosine 5'-[gamma-thio]triphosphate in the presence of Mg2+ nor ATP in the absence of Mg2+, increases transfer of ARF from the surrounding medium into the vesicle membranes. The specific vacuolar-type proton pump inhibitor bafilomycin B1 (10 nM), the protonophore carbonylcyanide m-chlorophenylhydrazone (10 microM), and replacement of chloride in the incubation buffer by acetate or nitrate resulted in an almost complete inhibition of the MgATP-dependent association of ARF to the vesicle membranes. The results demonstrate that redistribution of ARF to the vesicle membrane correlates with the intravesicular pH established by a vacuolar-type H(+)-ATPase. The intravesicular pH appears to be one mechanism by which certain low molecular weight GTP-binding proteins become relocated from the cytosol to their specific membrane vesicles.

ADP-Ribosylation Factors↗
PubMed1992

Association of a 19- and a 21-kDa GTP-binding protein to pancreatic microsomal vesicles is regulated by the intravesicular pH established by a vacuolar-type H(+)-ATPase.

Evidence suggests that certain ras-related small molecular weight GTP-binding proteins (smg-proteins) are involved in intracellular membrane trafficking and vesicle fusion. We have previously shown that intravesicular acidification due to a vacuolar-type H(+)-ATPase, which is Cl- dependent and highly sensitive to the specific inhibitor bafilomycin, enhances GTP-induced fusion of pancreatic microsomal vesicles (Hampe, W., Zimmermann, P., Schulz, I. 1990. FEBS Lett. 271:62-66). This process may involve function of smg-proteins. The present study shows that MgATP (2 mM), but neither MgATP gamma S nor ATP in the absence of Mg2+, increases association of 19- and 21-kDa smg-proteins to the vesicle membrane as monitored by their [ alpha-32P]GTP binding. The affinity of smg-proteins for [ alpha-32P]GTP was not altered by MgATP. Bafilomycin B1 (10(-8) M), the protonophore CCCP (10(-5) M), and replacement of Cl- in the incubation buffer by CH3COO- or NO3- resulted in an almost complete inhibition of the MgATP-dependent association of the 19- and 21-kDa smg-proteins to the vesicle membranes. Furthermore, the MgATP effect on both smg-proteins was found to be due to the intravesicular pH and not to the H+ gradient over the vesicle membrane. We conclude that association of a 19-kDa (immunologically identified as the ADP-ribosylation factor, arf) and a yet unidentified 21-kDa GTP-binding protein to vesicle membranes is regulated by the intravesicular pH established by a vacuolar-type H(+)-ATPase.

Adenosine Triphosphate↗
PubMed1992

Effects of agonists on p21ras and ras-related proteins in rat pancreatic acinar cells.

This study shows the presence of seven different low-molecular-weight GTP binding proteins (smg proteins) with molecular masses between 18 and 27 kDa in subfractions of rat pancreatic acinar cells. After stimulation of isolated intact and permeabilized pancreatic acinar cells with cholecystokinin octapeptide (CCK-OP), the diacylglycerol (DG) analogue 12-O-tetradecanoylphorbol 13-acetate (TPA), vasoactive intestinal peptide (VIP), adenosine 3',5'-cyclic monophosphate (cAMP), or guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), [alpha-32P]GTP binding to 21- to 22-kDa smg protein(s) in microsomal membranes (MM) was reduced, whereas the [alpha-32P]GTP binding to 23-kDa protein(s) was enhanced. In addition, prestimulation of permeabilized cells with GTP gamma S caused enhancement of [alpha-32P]GTP binding to a 19-kDa protein in MM [immunologically identified as the ADP-ribosylation factor (arf)]. In the presence of cytosol, direct addition of GTP gamma S to isolated MM resulted in an apparent translocation of the 19-kDa protein (arf) from the cytosol to membranes. This indicates increased association of arf with the membrane in its GTP-bound state. In CCK-OP-prestimulated acinar cells, [alpha-32P]GTP binding to plasma membrane-located 21- to 22-kDa proteins (immunologically identified as p21ras proteins) was enhanced, suggesting that there is an interrelationship between p21ras proteins and CCK receptors. Our results give evidence for a role of 19-kDa, 21- to 22-kDa, and 23-kDa smg proteins in cAMP-protein kinase A- and DG-protein kinase C-mediated stimulation of intracellular pathways in pancreatic acinar cells.

Animals↗
PubMed1992

Delayed activation of D-glucose transport in type II diabetes mellitus.

Peripheral insulin resistance is suggested to play an important role in the pathogenesis of type II diabetes mellitus. In this study we investigated insulin receptor binding, D-glucose transport under equilibrium conditions for insulin and the activation kinetics of insulin stimulated D-glucose transport in isolated human adipocytes from type II diabetics and healthy controls. While the insulin receptor binding affinity was not significantly different between both groups, basal and insulin stimulated glucose transport rates were reduced in adipocytes from type II diabetics compared to normal controls. The activation of D-glucose transport was significantly delayed in the diabetics, the time to achieve maximal transport rates was 7.7 +/- 1.1 vs. 4.2 +/- 1.4 min, respectively (p < 0.05). Thus a reduced velocity of glucose transport activation by insulin appears to be a further factor contributing to peripheral insulin resistance in type II diabetics.

Biological Transport↗
PubMed1991

Guanosine nucleotides modulate the inhibitory effect of brefeldin A on protein secretion.

Brefeldin A (BFA) causes rapid redistribution of Golgi proteins into the endoplasmic reticulum (ER), leaving no definable Golgi-apparatus, and blocks transport of proteins from the ER to distal secretory compartments of the cell. Using pulse-chase experiments the present study shows that BFA (1 microgram/ml) inhibits basal and CCK-stimulated protein secretion in isolated pancreatic acinar cells by 65 +/- 6% and 84 +/- 5%, respectively. In isolated permeabilized cells higher concentrations of BFA (30 micrograms/ml) were necessary to obtain inhibition of protein secretion. In parallel experiments protein secretion was stimulated by GTP (1 mM). BFA had no inhibitory effect on protein secretion in the presence of GTP, indicating that BFA might act on a GTP-binding protein. Investigating the effect of BFA on small molecular weight GTP-binding proteins we observed that [alpha-32P]GTP binding to a 21 kDa protein in a subcellular fraction enriched in ER was increased in the presence of BFA. We conclude that this 21 kDa and possibly also other GTP-binding proteins may be the molecular target of Brefeldin A in pancreatic acinar cells.

Animals↗
PubMed1991

[The influence of autonomic diabetic neuropathy and human atrial natriuretic peptide on adrenal gland function in postural changes].

To investigate the influence of postural changes on plasma renin activity (PRA), plasma levels of human atrial natriuretic peptide (hANP) and on aldosterone in diabetes mellitus and autonomic neuropathy, ten patients with diabetes mellitus and autonomic neuropathy and ten patients with diabetes mellitus but without autonomic neuropathy were studied. Ten healthy subjects served as controls. Patients and controls were in supine position for 60 minutes, then changed posture sequentially to sitting (90 minutes) and to upright position (15 minutes). In controls, PRA was increased upon sitting and in the upright position, while hANP was decreased. Patients with autonomic neuropathy differed from controls in impaired renin stimulation, whereas in patients without autonomic neuropathy PRA responses to postural changes were only slightly decreased. In both groups of patients, the normal hANP responsiveness to postural changes was lacking. There were no differences in aldosterone levels between patients and controls. In patients with high basal hANP levels due to elevated systolic blood pressure renin responses to postural changes were decreased in comparison to those patients with low basal hANP levels. Thus, in patients with diabetes mellitus increased hANP levels which are not decreased in response to upright standing may contribute to the development of hyporeninism and its sequelae.

Adult↗
PubMed1991

Interaction of caffeine-, IP3- and vanadate-sensitive Ca2+ pools in acinar cells of the exocrine pancreas.

Previous studies have shown the existence of functionally distinguishable inositol 1,4,5-trisphosphate- (IP3) sensitive and IP3-insensitive nonmitochondrial intracellular Ca2+ pools in acinar cells of the exocrine pancreas. For further characterization of Ca2+ pools, endoplasmic reticulum (ER) membrane vesicles were separated by Percoll gradient centrifugation which allowed us to distinguish five discrete fractions designated P1 to P5 from the top to the bottom of the gradient. Measuring Ca2+ uptake and Ca2+ release with a Ca2+ electrode, we could differentiate three nonmitochondrial intracellular Ca2+ pools: (i) an IP3-sensitive Ca2+ pool (IsCaP), vanadate- and caffeine-insensitive, (ii) a caffeine-sensitive Ca2+ pool (CasCaP), vanadate- and IP3-insensitive, and (iii) a vanadate-sensitive Ca2+ pool (VasCaP), neither IP3- nor caffeine-sensitive, into which Ca2+ uptake is mediated via a Ca2+ ATPase sensitive to vanadate at 10(-4) mol/liter. A fourth Ca2+ pool is neither IP3- nor caffeine- or vanadate-sensitive. Percoll fraction P1 contained essentially the IsCaP, CasCaP and VasCaP and was mainly used for studies on Ca2+ uptake and Ca2+ release. When membrane vesicles were incubated in the presence of caffeine (2 x 10(-2) mol/liter), Ca2+ uptake up to the steady state [Ca2+] did not appear to be altered as compared to the control Ca2+ uptake. However, in control vesicles spontaneous Ca2+ release occurred after the steady state had been reached, whereas caffeine-pretreated vesicles did not spontaneously release Ca2+. Addition of IP3 at steady state [Ca2+] induced similar Ca2+ release followed by Ca2+ reuptake in both caffeine-pretreated and control vesicles. However, when caffeine was acutely added at steady state, Ca2+ was released from all Ca2+ pools including the IsCaP. Following Ca2+ reuptake after IP3 had been added, a second addition of IP3 to control vesicles induced further but smaller Ca2+ release, and a third addition resulted in a steady Ca2+ efflux by which all Ca2+ that had been taken up was released. This steady Ca2+ release started at a Ca2+ concentration between 5.5-8 x 10(-7) mol/liter and could also be induced by the IP3 analogue inositol 1,4,5-trisphosphorothioate (IPS3) or by addition of Ca2+ itself. Ruthenium red (10(-5) mol/liter) inhibited both caffeine-induced as well as Ca2(+)-induced but not IP3-induced Ca2+ release. Heparin (100 micrograms/ml) inhibited IP3- but not caffeine-induced Ca2+ release. The data indicate the presence of at least three separate Ca2+ pools in pancreatic acinar cells: the IsCaP, CasCaP and VasCaP. During Ca2+ uptake these Ca2+ pools appear to be separate.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Chloro-7-nitrobenzofurazan↗
PubMed1991

Beat-to-beat variation of heart rate in diabetic patients with autonomic neuropathy and in completely cardiac denervated patients following orthotopic heart transplantation.

Dysfunction of the vagal nerve, an early symptom in the development of autonomic neuropathy, can be assessed reliably by the beat-to-beat variation in heart rate. Patients after a cardiac transplantation are a unique model to investigate the beat-to-beat variation of a completely denervated heart. Heart rate and the beat-to-beat variation during normal and deep respiration were investigated in diabetic subjects with an autonomic neuropathy (n = 10), age and sex matched healthy controls (n = 10) and cardiac transplanted patients (n = 10). Further studies during pharmacological blockade of the parasympathetic nervous system with atropine were performed. In the denervated heart the coefficient of variation of the beat-to-beat interval was 0.38 +/- 0.02% during normal respiration, compared to 1.32 +/- 0.13% (P less than 0.0001) and 2.56 +/- 0.13% (P less than 0.0001) in the diabetic and control subjects, respectively. Administration of atropine (2 mg intravenously) decreased the coefficient of variation of the RR-interval to 0.73 +/- 0.09% in the diabetic patients (P less than 0.0005) and to 0.67 +/- 0.07% in the controls (P less than 0.0001), whereas the coefficient of variation remained unaffected in the cardiac denervated patients (0.39 +/- 0.02%). In the three groups an almost parallel increase of the RR-variation was observed during deep respiration at a rate of 6 breaths/min (from 0.38 +/- 0.02% to 1.99 +/- 0.38% in cardiac transplanted patients, P less than 0.0025; from 1.32 +/- 0.13% to 3.10 +/- 0.43% in diabetic patients, P less than 0.0025; from 2.56 +/- 0.13% to 5.42 +/- 0.94% in healthy controls, P less than 0.005). We conclude that a beat-to-beat variation of heart rate is present in the completely denervated heart. This RR-variation can not be influenced by a pharmacological blockade of the parasympathetic nervous system with atropine. The beat-to-beat variation increases during deep respiration not only in healthy controls but also in diabetic patients with autonomic neuropathy (partially denervated hearts) and cardiac transplanted patients (completely denervated hearts). This indicates an intracardiac mechanism in the modulation of heart rate.

Atropine↗
PubMed1990

[Cystic polyposis of the stomach].

An X-ray contrast medium examination revealed extensive polyposis in the gastric fundus of a 66-year-old patient with intermittent heartburn. Physical examination and laboratory tests including carcinoembryonal antigen yielded no abnormal findings. Gastroduodenoscopy showed more than 100 polyps of about 5 mm diameter in the fundus and corpus of the stomach. Gastric mucosa was histologically intact. Numerous cysts lined by non-pathological epithelia were seen in the body and neck of the gastric glands. No polyps were found in the small bowel or colon. Since cystic polyposis does not tend to become malignant, no surgery was performed. Annual endoscopic controls, however, are recommended.

Aged↗
PubMed1990

In vitro activity of biosynthetic human diarginylinsulin.

In diarginylinsulin two arginine residues are located at the C-terminal end of the B-chain (ArgB31 and ArgB32). This accounts for a shift of the isoelectric point from pH 5.4 in native insulin to pH 7.0 in diarginylinsulin leading to pharmacodynamic characteristics of an intermediate acting insulin when administered s.c. as pH 4.0-5.0 solution. We have investigated insulin receptor binding and biological activity of biosynthetic human diarginylinsulin in human adipocytes and compared to native insulin and proinsulin. Association- and dissociation studies of insulin receptor binding revealed no differences for diarginylinsulin and native insulin. In competition studies under steady-state binding conditions, half-maximal displacement of tracer occurred at 352 +/- 33 pmol/l, 337 +/- 32 pmol/l and 3640 +/- 480 pmol/l for diarginylinsulin, insulin and proinsulin, respectively. The biologic potency of human diarginylinsulin was evaluated by the ability to stimulate D-glucose transport and by the assessment of the antilipolytic activity. Activation of D-glucose transport was half-maximal at 49.6 +/- 5.4 pmol/l (diarginylinsulin), 44.8 +/- 5.8 pmol/l (insulin) and at 476.7 +/- 134.3 pmol/l (proinsulin). Half-maximal inhibition of lipolysis occurred at 13.9 +/- 3.4 pmol/l, 15.4 +/- 2.9 pmol/l and 138.4 +/- 38.6 pmol/l, respectively. In conclusion, diarginylinsulin has almost identical insulin receptor binding characteristics and full biological activity in vitro compared to native insulin. This pharmacodynamically intermediate acting insulin preparation is therefore of potential therapeutical value.

Adipose Tissue↗
PubMed1990

In vivo evidence that human atrial natriuretic factor-(99-126) (hANF) stimulates parasympathetic activity in man.

In a double-blind study 8 healthy male subjects received 100 micrograms human atrial natriuretic facotr-(99-126) (hANF) and NaCl0.9% in random order on different days. Following hANF injection a significant increase in cardiac beat-to-beat variation was observed (4.65% vs 5.95%). This shows that in vivo human atrial natriuretic factor stimulates cardiac parasympathetic activity in man.

Adult↗