Inhibition of the high-affinity glucose transporter GLUT 1 affects the sensitivity to glucose in a hamster-derived pancreatic beta cell line (HIT)

Mouse embryonic stem cells established in physiological-glucose media express the high KM Glut2 glucose transporter expressed by normal embryos

Glut2 is one of the facilitative glucose transporters expressed by preimplantation and early postimplantation embryos. Glut2 is important for survival before embryonic day 10.5. The Glut2 KM (∼16 mmol/liter) is significantly higher than physiologic glucose concentrations (∼5.5 mmol/liter), suggesting that Glut2 normally performs some essential function other than glucose transport. Nevertheless, Glut2 efficiently transports glucose when extracellular glucose concentrations are above the Glut2 KM. Media containing 25 mmol/liter glucose are widely used to establish and propagate embryonic stem cells (ESCs). Glut2-mediated glucose uptake by embryos induces oxidative stress and can cause embryo cell death. Here we tested the hypothesis that low-glucose embryonic stem cells (LG-ESCs) isolated in physiological-glucose (5.5 mmol/liter) media express a functional Glut2 glucose transporter. LG-ESCs were compared with conventional D3 ESCs that had been cultured only in high-glucose media. LG-ESCs expressed Glut2 mRNA and protein at much higher levels than D3 ESCs, and 2-deoxyglucose transport by LG-ESCs, but not D3 ESCs, exhibited high Michaelis-Menten kinetics. Glucose at 25 mmol/liter induced oxidative stress in LG-ESCs and inhibited expression of Pax3, an embryo gene that is inhibited by hyperglycemia, in neuronal precursors derived from LG-ESCs. These effects were not observed in D3 ESCs. These findings demonstrate that ESCs isolated in physiological-glucose media retain a functional Glut2 transporter that is expressed by embryos. These cells are better suited to the study of metabolic regulation characteristic of the early embryo and may be advantageous for therapeutic applications.

In vitro evidences for glucosensing capacity and mechanisms in hypothalamus, hindbrain, and Brockmann bodies of rainbow trout

We aimed to support in vitro the glucosensing capacity observed in vivo in rainbow trout hypothalamus, hindbrain, and Brockmann bodies (BB) and to obtain preliminary evidence of the mechanisms involved. The response of parameters involved in the glucosensing capacity [hexokinase, hexokinase IV (glucokinase), and pyruvate kinase activities and glucose and glycogen levels] was assessed in these tissues incubated for 1 h with 2, 4, or 8 mM d-glucose alone (control) or with specific agonists/inhibitors of the steps involved in glucosensing capacity in mammals. These agents were a competitor for glucose phosphorylation (15 mM mannose), sulfonylurea receptor-1 effectors (500 μM tolbutamide or diazoxide), glycolytic intermediates (15 mM glycerol, lactate, or pyruvate), and inhibitors of glucose transport (10 μM cytochalasin B), glycolysis [20 mM 2-deoxy-d-glucose (2-DG)], and L-type calcium channel (1 μM nifedipine). Control incubations of the three tissues displayed increased glucose and glycogen levels and glucokinase activities in response to increased medium glucose, thus supporting our previous in vivo studies. Furthermore, critical components of the glucosensing mammalian machinery are apparently functioning in the three tissues. The responses in brain regions to all substances tested (except 2-DG and nifedipine) were similar to those observed in mammals, suggesting a similar glucosensing machinery. In contrast, in BB, only the effects of 2-DG, lactate, pyruvate, diazoxide, and nifedipine were similar to those of mammalian β-cells, suggesting that some of the components of the piscine glucosensing model are different than those of mammals. Such differences may relate to the importance of amino acids rather than glucose signaling in the trout BB.