Effects of plasma membrane Ca(2+)-ATPase overexpression upon D-glucose metabolism in insulin-producing BRIN-BD11 cells

Effects of high-level expression of A1-ATPase on H2 production in Thermococcus kodakarensis

The hyperthermophilic archaeon Thermococcus kodakarensis can grow on pyruvate or maltooligosaccharides through H₂ fermentation. H₂ production levels of members of the Thermococcales are high, and studies to improve their production potential have been reported. Although H₂ production is primary metabolism, here we aimed to partially uncouple cell growth and H₂ production of T. kodakarensis. Additional A₁-type ATPase genes were introduced into T. kodakarensis KU216 under the control of two promoters; the strong constitutive cell surface glycoprotein promoter, P_csg, and the sugar-inducible fructose-1,6-bisphosphate aldolase promoter, P_fba. Whereas cells with the A₁-type ATPase genes under the control of P_csg displayed only trace levels of growth, cells with P_fba (strain KUA-PF) displayed growth sufficient for further analysis. Increased levels of A₁-type ATPase protein were detected in KUA-PF cells grown on pyruvate or maltodextrin, when compared to the levels in the host strain KU216. The growth and H₂ production levels of strain KUA-PF with pyruvate or maltodextrin as a carbon and electron source were analyzed and compared to those of the host strain KU216. Compared to a small decrease in total H₂ production, significantly larger decreases in cell growth were observed, resulting in an increase in cell-specific H₂ production. Quantification of the substrate also revealed that ATPase overexpression led to increased cell-specific pyruvate and maltodextrin consumptions. The results clearly indicate that ATPase production results in partial uncoupling of cell growth and H₂ production in T. kodakarensis.

Effect of cytochalasin B on 3-O-[14C]-methyl-D-glucose or D-[U-14C]glucose handling by BRIN-BD11 cells

The present study aimed to investigate the effects of cytochalasin B (20 μM) on the uptake of 3-O-[¹⁴C]-methyl-D-glucose or D-[U-¹⁴C]glucose (8.3 mM each) by BRIN-BD11 cells. Taking into account the distribution space of tritiated water (³HOH), which was unexpectedly increased shortly after exposure of the cells to cytochalasin B and then progressively returned to its control values, and that of L-[1-¹⁴C]glucose, used as an extracellular marker, it was demonstrated that cytochalasin B caused a modest, but significant inhibition of the uptake of D-glucose and its non-metabolized analog by the BRIN-BD11 cells. These findings resemble those observed in acinar or ductal cells of the rat submaxillary gland and displayed a relative magnitude comparable to that found for the inhibition of D-glucose metabolism by cytochalasin B in purified pancreatic islet B cells. These findings reinforce the view that the primary site of action of cytochalasin B is located at the level of the plasma membrane.

Functional role of aquaglyceroporin 7 expression in the pancreatic beta-cell line BRIN-BD11

Both mouse and rat pancreatic islet beta-cells were recently found to express aquaglyceroporin 7 (AQP7). In the present study, the expression and role of AQP7 in the function of BRIN-BD11 cells were investigated. AQP7 mRNA and protein were detected by RT-PCR and Western blot analysis, respectively. In an isoosmolar medium, the net uptake of [2-(3)H]glycerol displayed an exponential time course reaching an equilibrium plateau value close to its extracellular concentration. Within 2 min of incubation in a hypotonic medium (caused by a 50 mM decrease in NaCl concentration), the [2-(3)H]glycerol uptake averaged 143.2 +/- 3.8% (n = 24; P < 0.001) of its control value in isotonic medium, declining thereafter consistently with previously demonstrated volume regulatory decrease. When isoosmolarity was restored by the addition of 100 mM urea to the hypotonic medium, [2-(3)H]glycerol uptake remained higher (112.1 +/- 2.8%, n = 24; P < 0.001) than its matched control under isotonic conditions, indicating rapid entry of urea and water. Insulin release by BRIN-BD11 cells was 3 times higher in hypotonic than in isotonic medium. When glycerol (100 mM) or urea (100 mM) were incorporated in the hypotonic medium, the insulin release remained significantly higher than that found in the control isotonic medium, averaging respectively 120.2 +/- 4.2 and 107.0 +/- 3.8% of the paired value recorded in the hypotonic medium. These findings document the rapid entry of glycerol and urea in BRIN-BD11 cells, likely mediated by AQP7.

Direct effects of eicosapentaenoic and docosahexaenoic acids on phospholipid and triglyceride fatty acid pattern, glucose metabolism, 86rubidium net uptake and insulin release in BRIN-BD11 cells

The long-term metabolic and functional effects of a dietary deprivation of long-chain polyunsaturated omega3 fatty acids were recently investigated in second-generation omega3-depleted rats. This study represents the first attempt to explore the direct, but not immediate, effects of omega3 fatty acids on insulin-producing cells. For this purpose, BRIN-BD11 cells were cultured for 24 h in the absence or presence of both C20:5omega3 and C22:6omega3 (50 microM each) and, thereafter, examined for their phospholipid and triglyceride fatty acid pattern, and their metabolic, ionic, and secretory responses to D: -glucose and/or non-nutrient insulinotropic agents. The prior culture in the presence of the two omega3 fatty acids provoked an enrichment of cell lipids in such omega3 fatty acids, changes in the phospholipid fatty acid pattern of long-chain polyunsaturated omega6 fatty acids as well as saturated and monodesaturated fatty acids, and cell steatosis. It minimized the relative increase in D: -[5-(3)H]glucose utilization and D: -[U-(14)C]glucose oxidation otherwise resulting from an increase in the concentration of the hexose from 1.1 to 11.1 mM. It also minimized the changes in (86)Rb(+) net uptake otherwise provoked by rises in D: -glucose concentration and decreased the absolute values for insulin output. It is concluded that the major changes in metabolic, cationic, and secretory behavior of the omega3-enriched BRIN-BD11 cells are paradoxically similar to those encountered in pancreatic islets from omega3-depleted rats and, in both cases, possibly attributable to a phenomenon of lipotoxicity.