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Articles by F. Lang
Total Records ( 15 ) for F. Lang
  K. M Boini , D Graf , A. M Hennige , S Koka , D. S Kempe , K Wang , T. F Ackermann , M Foller , V Vallon , K Pfeifer , E Schleicher , S Ullrich , H. U Haring , D Haussinger and F. Lang
  The pore-forming K+-channel -subunit KCNQ1 is expressed in a wide variety of tissues including heart, skeletal muscle, liver, and epithelia. Most recent evidence revealed an association of the KCNQ1 gene with the susceptibility to type 2 diabetes. KCNQ1 participates in the regulation of cell volume, which is, in turn, critically important for the regulation of metabolism by insulin. The present study explored the influence of KCNQ1 on insulin-induced cellular K+ uptake and glucose metabolism. Insulin (100 nM)-induced K+ uptake was determined in isolated perfused livers from KCNQ1-deficient mice (kcnq1–/–) and their wild-type littermates (kcnq1+/+). Moreover, plasma glucose and insulin levels, intraperitoneal glucose (3 g/kg) tolerance, insulin (0.15 U/kg)-induced hypoglycemia, and peripheral uptake of radiolabeled 3H-deoxy-glucose were determined in both genotypes. Insulin-stimulated hepatocellular K+ uptake was significantly more sustained in isolated perfused livers from kcnq1–/– mice than from kcnq1+/+mice. The decline of plasma glucose concentration following an intraperitoneal injection of insulin was again significantly more sustained in kcnq1–/– than in kcnq1+/+ mice. Both fasted and nonfasted plasma glucose and insulin concentrations were significantly lower in kcnq1–/– than in kcnq1+/+mice. Following an intraperitoneal glucose injection, the peak plasma glucose concentration was significantly lower in kcnq1–/– than in kcnq1+/+mice. Uptake of 3H-deoxy-glucose into skeletal muscle, liver, kidney and lung tissue was significantly higher in kcnq1–/– than in kcnq1+/+mice. In conclusion, KCNQ1 counteracts the stimulation of cellular K+ uptake by insulin and thereby influences K+-dependent insulin signaling on glucose metabolism. The observations indicate that KCNQ1 is a novel molecule affecting insulin sensitivity of glucose metabolism.
  S Gatidis , O Borst , M Foller and F. Lang

Blood passing the renal medulla enters a strongly hypertonic environment challenging functional properties and survival of blood cells. In erythrocytes, exposure to hyperosmotic shock stimulates Ca2+ entry and ceramide formation with subsequent cell membrane scrambling, an effect partially reversed by high concentrations of Cl or urea. Cell membrane scrambling with phosphatidylserine exposure is part of the procoagulant phenotype of platelets. Coagulation in the hypertonic renal medulla would jeopardize blood flow in the vasa recta. The present study thus explored whether hypertonic environment and urea modify phosphatidylserine exposure of human platelets. FACS analysis was employed to estimate cytosolic Ca2+ activity with Fluo3 fluorescence, ceramide formation, P-selectin, and glycoprotein IIb/IIIa activation with fluorescent antibodies and phosphatidylserine exposure with annexin V-binding. The spontaneous platelet aggregation was measured by impedance aggregometry. Hyperosmotic shock (addition of 500 mM sucrose or 250 mM NaCl) significantly enhanced cytosolic Ca2+ activity, ceramide formation, phosphatidylserine exposure, platelet degranulation, and aggregability. Addition of 500 mM urea to isotonic saline did not significantly modify cytosolic Ca2+ activity, ceramide abundance, or annexin V-binding but significantly blunted the respective effects of hypertonic shock following addition of 500 mM sucrose. In isotonic solutions, both ceramide (20 µM) and Ca2+ ionophore ionomycin (0.5 µM) increased annexin V-binding, effects again significantly blunted by 500 mM urea. Moreover, oxidative stress by addition of 0.5 mM peroxynitrite increased cytosolic Ca2+ activity and triggered annexin V-binding, effects again blunted in the presence of 500 mM urea. The observations reveal that hyperosmotic shock and oxidative stress trigger a procoagulant platelet phenotype, an effect blunted by the presence of high urea concentrations.

  I. M Zemtsova , N Heise , H Frohlich , S. M Qadri , Y Kucherenko , K. M Boini , D Pearce , E Shumilina and F. Lang

Previous studies have shown that pharmacological inhibition of the phosphoinositol-3 (PI3) kinase disrupts the activation of mast cells. Through phosphoinositide-dependent kinase PDK1, PI3 kinase activates the serum- and glucocorticoid-inducible kinase 3 (SGK3). The present study explored the role of SGK3 in mast cell function. Mast cells were isolated and cultured from bone marrow (BMMCs) of gene-targeted mice lacking SGK3 (sgk3–/–) and their wild-type littermates (sgk3+/+). BMMC numbers in the ear conch were similar in both genotypes. Stimulation with IgE and cognate antigen triggered the release of intracellular Ca2+ and entry of extracellular Ca2+. Influx of extracellular Ca2+ but not Ca2+ release from intracellular stores was significantly blunted in sgk3–/– BMMCs compared with sgk3+/+ BMMCs. Antigen stimulation further led to a rapid increase of a K+-selective conductance in sgk3+/+ BMMCs, an effect again blunted in sgk3–/– BMMCs. In contrast, the Ca2+ ionophore ionomycin activated K+ currents to a similar extent in sgk3–/– and in sgk3+/+ BMMCs. β-Hexosaminidase release, triggered by antigen stimulation, was also significantly decreased in sgk3–/– BMMCs. IgE-dependent anaphylaxis measured as a sharp decrease in body temperature upon injection of DNP-HSA antigen was again significantly blunted in sgk3–/– compared with sgk3+/+ mice. Serum histamine levels measured 30 min after induction of an anaphylactic reaction were significantly lower in sgk3–/– than in sgk3+/+ mice. In conclusion, both in vitro and in vivo function of BMMCs are impaired in gene targeted mice lacking SGK3. Thus SGK3 is critical for proper mast cell function.

  L Tyan , M Sopjani , M Dermaku Sopjani , E Schmid , W Yang , N. T Xuan , E Shumilina and F. Lang

Rapamycin, an inhibitor of the serine/threonine kinase mammalian target of rapamycin (mTOR), is a widely used immunosuppressive drug. Rapamycin affects the function of dendritic cells (DCs), antigen-presenting cells participating in the initiation of primary immune responses and the establishment of immunological memory. Voltage-gated K+ (Kv) channels are expressed in and impact on the function of DCs. The present study explored whether rapamycin influences Kv channels in DCs. To this end, DCs were isolated from murine bone marrow and ion channel activity was determined by whole cell patch clamp. To more directly analyze an effect of mTOR on Kv channel activity, Kv1.3 and Kv1.5 were expressed in Xenopus oocytes with or without the additional expression of mTOR and voltage-gated currents were determined by dual-electrode voltage clamp. As a result, preincubation with rapamycin (0–50 nM) led to a gradual decline of Kv currents in DCs, reaching statistical significance within 6 h and 50 nM of rapamycin. Rapamycin accelerated Kv channel inactivation. Coexpression of mTOR upregulated Kv1.3 and Kv1.5 currents in Xenopus oocytes. Furthermore, mTOR accelerated Kv1.3 channel activation and slowed down Kv1.3 channel inactivation. In conclusion, mTOR stimulates Kv channels, an effect contributing to the immunomodulating properties of rapamycin in DCs.

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