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Articles by S Koka
Total Records ( 13 ) for S Koka
  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.
  M Ghashghaeinia , D Bobbala , T Wieder , S Koka , J Bruck , B Fehrenbacher , M Rocken , M Schaller , F Lang and K. Ghoreschi

The balance between GSH-levels and oxidative stress is critical for cell survival. The GSH-levels of erythrocytes are dramatically decreased during infection with Plasmodium spp. We therefore investigated the consequences of targeting GSH for erythrocyte and Plasmodium survival in vitro and in vivo using dimethylfumarate (DMF) at therapeutically established dosage. We first show that noninfected red blood cells (RBC) exposed to DMF undergo changes typical of apoptosis or eryptosis, such as cell shrinkage and cell membrane scrambling with subsequent phosphatidylserine (PS) exposure. DMF did not induce appreciable hemolysis. DMF-triggered PS exposure was mediated by intracellular GSH depletion and reversed by the antioxidative N-acetyl-l-cysteine. DMF treatment controlled intraerythrocyte DNA amplification and in vitro parasitemia of Plasmodium falciparum-infected RBC. In vivo, DMF treatment had no effect on RBC count or GSH levels in noninfected mice. Consistent with its effects on infected RBC, DMF treatment abrogated parasitemia and enhanced the survival of mice infected with Plasmodium berghei from 0% to 60%. In conclusion, DMF sensitizes the erythrocytes to the effect of Plasmodium infection on PS exposure, thus accelerating the clearance of infected erythrocytes. Accordingly, DMF treatment favorably influences the clinical course of malaria. As DMF targets mechanisms within the host cell, it is not likely to generate resistance of the pathogen.

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