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Biomedical subjects

G Drews

Publications and source records attributed to G Drews.

At least 19 recordsLinked to original sources
PubMed2005

Crosstalk between membrane potential and cytosolic Ca2+ concentration in beta cells from Sur1-/- mice.

AIMS/HYPOTHESIS: Islets or beta cells from Sur1(-/-) mice were used to determine whether changes in plasma membrane potential (V(m)) remain coupled to changes in cytosolic Ca(2+) ([Ca(2+)](i)) in the absence of K(ATP) channels and thus provide a triggering signal for insulin secretion. The study also sought to elucidate whether [Ca(2+)](i) influences oscillations in V(m) in sur1(-/-) beta cells. METHODS: Plasma membrane potential and ion currents were measured with microelectrodes and the patch-clamp technique. [Ca(2+)](i) was monitored with the fluorescent dye fura-2. Insulin secretion from isolated islets was determined by static incubations. RESULTS: Membrane depolarisation of Sur1(-/-) islets by arginine or increased extracellular K(+), elevated [Ca(2+)](i) and augmented insulin secretion. Oligomycin completely abolished glucose-stimulated insulin release from Sur1(-/-) islets. Oscillations in V(m) were influenced by [Ca(2+)](i) as follows: (1) elevation of extracellular Ca(2+) lengthened phases of membrane hyperpolarisation; (2) simulating a burst of action potentials induced a Ca(2+)-dependent outward current that was augmented by increased Ca(2+) influx through L-type Ca(2+) channels; (3) Ca(2+) depletion of intracellular stores by cyclopiazonic acid increased the burst frequency in Sur1(-/-) islets, elevating [Ca(2+)](i) and insulin secretion; (4) store depletion activated a Ca(2+) influx that was not inhibitable by the L-type Ca(2+) channel blocker D600. CONCLUSIONS/INTERPRETATION: Although V(m) is largely uncoupled from glucose metabolism in the absence of K(ATP) channels, increased electrical activity leads to elevations of [Ca(2+)](i) that are sufficient to stimulate insulin secretion. In Sur1(-/-) beta cells, [Ca(2+)](i) exerts feedback mechanisms on V(m) by activating a hyperpolarising outward current and by depolarising V(m) via store-operated ion channels.

ATP-Binding Cassette Transporters↗
PubMed2004

Direct interference of HIV protease inhibitors with pancreatic beta-cell function.

The aim of the present study was to evaluate whether HIV protease inhibitors directly interfere with stimulus-secretion coupling in pancreatic beta-cells. Insulin secretion was determined by a radioimmunoassay (RIA), cytosolic free Ca2+ concentration ([Ca2+]c) with the fluorescence dye fura-2 and whole-cell membrane currents with the patch-clamp technique. Glucose-induced insulin secretion was inhibited in a concentration-dependent manner by ritonavir and nelfinavir but not by indinavir. Ritonavir and nelfinavir lowered [Ca2+]c in the presence of a stimulatory glucose concentration whereas indinavir again had no effect. Ritonavir and nelfinavir completely inhibited the effect of tolbutamide, which normally increases [Ca2+]c by blocking KATP channels. This observation points to an action of both drugs on KATP channels or a step distal to these channels in stimulus-secretion coupling. Ritonavir was used to further evaluate the direct effects of HIV protease inhibitors on beta-cell ion channel currents. Unexpectedly, ritonavir inhibited neither the whole-cell KATP current nor the whole-cell L-type Ca2+ current. Tolbutamide almost completely suppressed the KATP current in the presence of ritonavir excluding that ritonavir alters the tolbutamide sensitivity of the KATP channel. Ritonavir increased the length and decreased the frequency of glucose-induced action potentials. This effect can be attributed to inhibition of voltage-dependent K+ currents. Intracellular stores seem not to be involved in the ritonavir-induced lowering of [Ca2+]c. In conclusion, different HIV protease inhibitors surprisingly reveal distinct effects on insulin secretion. Ritonavir inhibits insulin secretion by lowering [Ca2+]c but this effect is evidently independent of the opening of KATP channels or the closure of voltage-dependent Ca2+ channels, which are commonly considered to play a key role in stimulus-secretion coupling.

Animals↗
PubMed2004

Oscillations of membrane potential and cytosolic Ca(2+) concentration in SUR1(-/-) beta cells.

AIMS/HYPOTHESIS: SUR1(ABCC8)(-/-) mice lacking functional K(ATP) channels are an appropriate model to test the significance of K(ATP) channels in beta-cell function. We examined how this gene deletion interferes with stimulus-secretion coupling. We tested the influence of metabolic inhibition and galanin, whose mode of action is controversial. METHODS: Plasma membrane potential (Vm) and currents were measured with microelectrodes or the patch-clamp technique; cytosolic Ca(2+) concentrations ([Ca(2+)](c)) and mitochondrial membrane potential (DeltaPsi) were measured using fluorescent dyes. RESULTS: In contrast to the controls, SUR1(-/-) beta cells showed electrical activity even at a low glucose concentration. Continuous spike activity was measured with the patch-clamp technique, but with microelectrodes slow oscillations in Vm consisting of bursts of Ca(2+)-dependent action potentials were detected. [Ca(2+)](c) showed various patterns of oscillations or a sustained increase. Sodium azide did not hyperpolarize SUR1(-/-) beta cells. The depolarization of DeltaPsi evoked by sodium azide was significantly lower in SUR1(-/-) than SUR1(+/+) cells. Galanin transiently decreased action potential frequency and [Ca(2+)](c) in cells from both SUR1(-/-) and SUR1(+/+) mice. CONCLUSION/INTERPRETATION: The strong dependence of Vm and [Ca(2+)](c) on glucose concentration observed in SUR1(+/+) beta cells is disrupted in the knock-out cells. This demonstrates that both parameters oscillate in the absence of functional K(ATP) channels. The lack of effect of metabolic inhibition by sodium azide shows that in SUR1(-/-) beta cells changes in ATP/ADP no longer link glucose metabolism and Vm. The results with galanin suggest that this peptide affects beta cells independently of K(ATP) currents and thus could contribute to the regulation of beta-cell function in SUR1(-/-) animals.

ATP-Binding Cassette Transporters↗
PubMed2001

Auxiliary partial orthotopic liver transplantation: treatment of acute liver failure in a new rat model.

BACKGROUND AND AIMS: Liver regeneration and functional interaction between native liver and graft after auxiliary partial orthotopic liver transplantation (APOLT) are not entirely understood and, therefore, require an experimental model simulating the clinical features of acute liver failure (ALF) and the surgical technique of APOLT. MATERIALS AND METHODS: ALF was induced by subtotal hepatectomy in 50 Lewis rats (200-250 g). Sham operation (I), ALF without treatment (II), ALF with portocaval shunt for decreasing blood flow of the remnant liver (III), and ALF treated by APOLT (IV) were performed. The auxiliary graft represented a left donor liver lobe which was orthotopically implanted using a microsurgical technique including reconstruction of the graft artery and internal biliary drainage. Operative outcomes, serum chemistry and histopathological findings were examined up to the 14th day. RESULTS: ALF without treatment (groups II and III) led to a small droplet fatty degeneration in the hepatocytes and a significant increase of liver parameters until the death of the animals within the first two postoperative days ( P<0.05). After APOLT (group IV), 80% of the animals survived up to the 14th day, revealing significantly decreased liver parameters ( P<0.05), a well-perfused graft and an up to five times increased native liver size with normal architecture. CONCLUSION: This new rat model simulates the clinical features of an ALF treated by APOLT and is especially interesting for further basic research on the interaction between native liver and auxiliary graft after APOLT.

Animals↗
PubMed2001

Stimulation of leukotriene synthesis in intact polymorphonuclear cells by the 5-lipoxygenase inhibitor 3-oxo-tirucallic acid.

Commercially available extracts from Boswellia serrata resin used as anti-inflammatory drugs or phytonutrients show paradoxical concentration-dependent potentiating and inhibitory actions on 5-lipoxygenase (5-LO) product synthesis in stimulated PMNs. In our attempt to characterize the stimulating constituents, we identified the tetracyclic triterpene 3-oxo-tirucallic acid (3-oxo-TA), which, in the range from 2.5 to 15 microM, enhanced 5-LO product formation in ionophore-challenged polymorphonuclear cells (PMNs) (e.g., from 1981 +/- 177 to 3042 +/- 208 pmol at 10 microM 3-oxo-TA), and initiated Ca(2+) mobilization, MEK-1/2 phosphorylation, 5-LO translocation, and 5-LO product formation in resting cells (534 +/- 394 pmol/5 x 10(6) PMNs). In cell-free 5-LO assays, 3-oxo-TA acted only inhibitory (IC(50) value of about 3 microM), demonstrating the pivotal role of intact cell structure for its activating property. In 3-oxo-TA-challenged PMNs, the mitogen-activated protein kinase kinase (MEK)-1/2 inhibitor PD098059 abolished 5-LO product formation, along with inhibition of MEK-1/2 phosphorylation and 5-LO translocation. The 3-acetoxy derivative of 3-oxo-TA acted like 3-oxo-TA in intact PMNs, whereas 3-hydroxy-TA barely stimulated MEK phosphorylation in resting cells and showed only inhibition on ionophore-induced 5-LO product synthesis. Steroid-type tetracycles neither induced 5-LO activation nor had enhancing or inhibitory effects. In summary, defined natural tetracyclic triterpenes, which act as inhibitors of the 5-LO in the cell-free assay, initiate 5-LO activation by a MEK-inhibitor sensitive mechanism and potentiate stimulated product synthesis in intact cells. Because TAs contribute significantly to the overall biological effects of B. serrata resin extracts, special precaution for standardization is recommended when using B. serrata preparations as drugs or dietary supplements.

Arachidonate 5-Lipoxygenase↗
PubMed2001

Diabetogenic effect of cyclosporin A is mediated by interference with mitochondrial function of pancreatic B-cells.

Treatment of patients after organ transplantation with the immunosuppressive drug cyclosporin A (CsA) is often accompanied by impaired glucose tolerance, thus promoting the development of diabetes mellitus. In the present article we show that 2 to 5 microM CsA diminishes glucose-induced insulin secretion of isolated mouse pancreatic islets in vitro by inhibiting glucose-stimulated oscillations of the cytoplasmic free-Ca(2+) concentration [Ca(2+)](c). This effect is not due to an inhibition of calcineurin, which mediates the immunosuppressive effect of CsA, because other calcineurin inhibitors, deltamethrin and tacrolimus, did not affect the oscillations in [Ca(2+)](c) of the B-cells. The CsA-induced decrease in [Ca(2+)](c) to basal values was not caused by a direct inhibition of L-type Ca(2+) channels. CsA is known to be a potent inhibitor of the mitochondrial permeability transition pore (PTP), which we recently suggested to be involved in the regulation of oscillations. Consequently, CsA also inhibited the oscillations of the cell membrane potential, and it is shown that these effects could not be ascribed to cellular ATP depletion. However, the mitochondrial membrane potential Delta Psi was affected by CsA by inhibiting the oscillations in Delta Psi. Interestingly, the observed reduction in [Ca(2+)](c) could be counteracted by the K(+)(ATP) channel blocker tolbutamide, indicating that the stimulus-secretion coupling was interrupted before the closure of K(+)(ATP) channels. It is concluded that CsA alters B-cell function by inhibiting the mitochondrial PTP. This terminates the oscillatory activity that is indispensable for adequate insulin secretion. Thus, CsA acts on different targets to induce the immunosuppressive and the diabetogenic effect.

Adenosine Triphosphate↗
PubMed2000

Contrasting effects of alloxan on islets and single mouse pancreatic beta-cells.

Alloxan is used to induce diabetes in animals; however, the underlying mechanisms are still a matter of debate. Alloxan evoked a rapid hyperpolarization of the plasma membrane potential and suppressed electrical activity elicited by 15 mM glucose, thus terminating voltage-dependent Ca(2+) influx. Accordingly, glucose-induced oscillations in intracellular free Ca(2+) concentration were abolished. The effect of alloxan on membrane potential could not be reversed by glucose but was reversed by tolbutamide. However, the sensitivity to tolbutamide was decreased after treatment of the cells with alloxan. These effects closely resemble those described earlier for H(2)O(2). H(2)O(2) and alloxan decreased the mitochondrial membrane potential, indicating a decrease in ATP production and thus interference with cell metabolism. A decrease in ATP synthesis would explain the plasma membrane hyperpolarization observed in intact islets, reflecting the activation of ATP-dependent K(+) channels. Surprisingly, alloxan inhibited the whole-cell K(+)(ATP) current measured in single cells and the single-channel K(+)(ATP) current registered in excised patches. This inhibitory effect of alloxan is not mediated by changes in cell metabolism but seems to be due to direct interactions with the K(+)(ATP) channels via thiol-group oxidation. We have monitored the appearance of reactive oxygen species in single cells and islets treated with alloxan and H(2)O(2) for comparison. In contrast to H(2)O(2), alloxan induced the appearance of measurable reactive oxygen species only in islets but not in single cells. The results show that alloxan evokes different effects in islets and single cells, giving a possible explanation for inconsistent results reported in the past. It is concluded that alloxan exerts its diabetogenic effect by the production of H(2)O(2) in intact islets.

Alloxan↗
PubMed2000

Dual effect of NO on K(+)(ATP) current of mouse pancreatic B-cells: stimulation by deenergizing mitochondria and inhibition by direct interaction with the channel.

Nitric oxide (NO) is assumed to contribute to the impairment of B-cell function in type 1 diabetes mellitus (IDDM). In the present paper we show that in mouse B-cells with intact metabolism authentic NO (20 microM) led to a biphasic effect on the K(+)(ATP) current, namely a transient increase and a consecutive almost complete inhibition. This resembles closely the effect that we have observed previously with the NO donor S-nitrosocysteine (SNOC, 1 mM) suggesting that merely NO caused both phases of this effect. We now demonstrate that the rise in the current amplitude was accompanied by a depolarization of the mitochondrial membrane potential DeltaPsi and a concomitant reduction in the ATP/ADP ratio. Thus, it seems likely that the increase in current amplitude is due to the interference of NO with cell metabolism. The subsequent inhibition of the K(+)(ATP) current is assumed to be caused by a direct effect on the channel since K(+)(ATP) single channel current activity measured in excised patches was strongly reduced by authentic NO and SNOC. Our data reveal new insights into the mechanisms underlying the biphasic action of NO on K(+)(ATP) channels in pancreatic B-cells.

Adenosine Diphosphate↗
PubMed2000

Parallel oscillations of intracellular calcium activity and mitochondrial membrane potential in mouse pancreatic B-cells.

Insulin secretion in normal B-cells is pulsatile, a consequence of oscillations in the cell membrane potential (MP) and cytosolic calcium activity ([Ca(2+)](c)). We simultaneously monitored glucose-induced changes in [Ca(2+)](c) and in the mitochondrial membrane potential DeltaPsi, as a measure for ATP generation. Increasing the glucose concentration from 0.5 to 15 mM led to the well-known hyperpolarization of DeltaPsi and ATP-dependent lowering of [Ca(2+)](c). However, as soon as [Ca(2+)](c) rose due to the opening of voltage-dependent Ca(2+) channels, DeltaPsi depolarized and thereafter oscillations in [Ca(2+)](c) were parallel to oscillations in DeltaPsi. A depolarization or oscillations of DeltaPsi cannot be evoked by a substimulatory glucose concentration, but Ca(2+) influx provoked by 30 mM KCl was followed by a depolarization of DeltaPsi. The following feedback loop is suggested: Glucose metabolism via mitochondrial ATP production and closure of K(+)(ATP) channels induces an increase in [Ca(2+)](c). The rise in [Ca(2+)](c) in turn decreases ATP synthesis by depolarizing DeltaPsi, thus transiently terminating Ca(2+) influx.

Animals↗
PubMed2000

The roots of microbiology and the influence of Ferdinand Cohn on microbiology of the 19th century.

The beginning of modern microbiology can be traced back to the 1870s, and it was based on the development of new concepts that originated during the two preceding centuries on the role of microorganisms, new experimental methods, and discoveries in chemistry, physics, and evolutionary cell biology. The crucial progress was the isolation and growth on solid media of clone cultures arising from single cells and the demonstration that these pure cultures have specific, inheritable characteristics and metabolic capacities. The doctrine of the spontaneous generation of microorganisms, which stimulated research for a century, lost its role as an important concept. Microorganisms were discovered to be causative agents of infectious diseases and of specific metabolic processes. Microscopy techniques advanced studies on microorganisms. The discovery of sexuality and development in microorganisms and Darwin's theory of evolution contributed to the founding of microbiology as a science. Ferdinand Cohn (1828-1898), a pioneer in the developmental biology of lower plants, considerably promoted the taxonomy and physiology of bacteria, discovered the heat-resistant endospores of bacilli, and was active in applied microbiology.

Bacteria↗
PubMed1999

Interference of H2O2 with stimulus-secretion coupling in mouse pancreatic beta-cells.

1. We have reported previously that in mouse pancreatic beta-cells H2O2 hyperpolarizes the membrane and increases the ATP-sensitive K+ current recorded in the perforated patch configuration of the patch-clamp technique. The present study was undertaken to elucidate the underlying mechanisms. 2. The intracellular ATP concentration measured by chemoluminescence was reduced by H2O2. The ADP concentration increased in parallel during the first 10 min, resulting in a pronounced decrease in the ATP/ADP ratio. 3. Consistent with these results, glucose-stimulated insulin secretion from isolated islets was inhibited by H2O2. 4. Membrane hyperpolarization measured with intracellular microelectrodes in intact islets and inhibition of insulin secretion were counteracted by tolbutamide, indicating that the channels are still responsive to inhibitors and that the ATP concentration is not too low to trigger exocytosis. However, the sensitivity of the beta-cells to tolbutamide was reduced after treatment with H2O2. 5. H2O2 increased the intracellular Ca2+ activity ([Ca2+]i) in a biphasic manner. A first transient rise in [Ca2+]i due to mobilization of Ca2+ from intracellular stores was followed by a sustained increase, which was at least partly dependent on Ca2+ influx. The first phase seems to reflect Ca2+ mobilization from mitochondria. 6. Our results demonstrate that H2O2 interferes with glucose metabolism, which influences the membrane potential and ATP-sensitive K+ current via the intracellular concentration of ATP. These events finally lead to an inhibition of insulin secretion despite an increase in [Ca2+]i.

Adenosine Triphosphate↗
PubMed1999

The LHIalpha and LHIIalpha complexes in association with phospholipids are able to be inserted in heavy membranes of Rhodobacter capsulatus B10.

We show in this paper that a complex constituted by phospholipids and LHI and LHII alpha polypeptides was inserted in a heavy membrane fraction in a nonextractable form, indicating a transmembrane localization. The best accepting membranes originated from aerobically grown cells. Addition of ATP during the insertion inhibited this reaction 25 to 30% in heavy membranes isolated from aerobically grown cells (HMaer) and a higher inhibition (60 to 65%) was detected when using heavy membranes isolated from photosynthetically grown cells (HMpho). Purification by gel filtration of a crude Na2CO3 extract yielded three phosphate-labeled fractions. Two of them contained protein and phospholipids in a stable association. However, only fractions containing phosphatidylethanolamine were shown to be reconstituted. The third radioactive fraction contained labeled ATP and protein, but no phospholipids and could not be reassociated to the heavy membranes of any origin. A model for the insertion of the LH polypeptides is presented in which the recently synthesized polypeptides are phosphorylated and become associated to anionic phospholipids. The interaction of this complex to the membrane spontaneously leads to stable insertion.

Bacterial Proteins↗
PubMed1999

Malignant schwannoma and late-onset form of neurofibromatosis (NF-VII type) in a patient with skeletal manifestations.

INTRODUCTION: Von Recklinghausen's neurofibromatosis is known to occur with markedly variable expressivity. Nevertheless, cases that do not feature characteristic findings are uncommon. CASE: We report an extremely rare, sporadic case of neurofibromatosis, exclusively represented in the skeleton of a 49-year-old woman. The late onset of the disease and the absence of common diagnostic criteria permit us to classify it as neurofibromatosis type VII. Additionally, the disease was complicated by early malignant transformation of a thoracic neurinoma, which was removed by a wide local resection. Two years after surgery, the patient developed local recurrence and liver metastases. She died a few months later despite aggressive chemotherapy.

Bone Neoplasms↗
PubMed1999

Ca2+/calmodulin inhibition and phospholipase C-linked Ca2+ Signaling in clonal beta-cells.

Neurotransmitters and hormones, such as arginine vasopressin (AVP) and bombesin, evoke frequency-modulated repetitive Ca2+ transients in insulin-secreting HIT-T15 cells by binding to receptors linked to phospholipase C (PLC). The role of calmodulin (CaM)-dependent mechanisms in the generation of PLC-linked Ca2+ transients was investigated by use of the naphthalenesulfonamide CaM antagonists W-7 and W-13 and their dechlorinated control analogs W-5 and W-12. W-7 (10-30 microM) and W-13 (30-100 microM), but not W-5 (100 microM) and W-12 (300 microM), reversibly inhibited the AVP- and bombesin-induced Ca2+ transients. As the generation of PLC-linked Ca2+ transients requires mobilization of internal Ca2+ and Ca2+ influx through voltage-sensitive (VSCC) and -insensitive (VICC) Ca2+ channels, the effects of the W compounds on these processes were further investigated. First, W-7 dose dependently diminished K+ (45 mM)-induced Ca2+ signals (IC50, approximately 25 microM), and W-13 (100 microM) reduced the K+ (45 mM)-induced [Ca2+]i rise by about 40-60%, whereas W-5 (100 microM) and W-12 (300 microM) had no effect. In addition, W-7 (100 microM) inhibited whole cell Ca2+ currents in mouse beta-cells by about 60%. Second, pretreatment of cells (5 min) with W-7 (30 microM), but not W-5 (30 microM), inhibited agonist-induced internal Ca2+ mobilization by about 75% in Ca2+-free medium. Neither W-7 (30 microM) nor W-5 (30 microM) affected AVP (100 nM)-stimulated formation of IP3. Third, capacitative Ca2+ influx through VICC activated by thapsigargin (2 microM) in the presence of verapamil (50 microM) was inhibited by W-7 (30 microM) but not by W-5 (30 microM). As all of the W compound effects corresponded well to their reported anticalmodulin activity, a specific anticalmodulin action can be assumed. Thus, Ca2+ via activation of CaM-dependent processes could provide positive feedback on the generation of PLC-linked Ca2+ transients in HIT-T15 cells. This appears to involve CaM-dependent regulation of both mobilization of internal Ca2+ and Ca2+ influx through VSCC and VICC.

Animals↗