Glucose tolerance factor stimulates 3-O-methylglucose transport into isolated rat adipocytes

Glucose tolerance factor partially purified from yeast extract powder stimulated [U-14C]-D-glucose uptake to a level 5.6 times greater than the basal level in the absence of insulin in isolated adipocytes prepared from rats fed with normal laboratory chow. The factor also stimulated 3-O-methylglucose transport 2.2-fold from the basal level in the absence of insulin, but not in the presence of 8 nM insulin. Kinetic analysis revealed that glucose tolerance factor increased 3-O-methylglucose transport by decreasing the Ks value for 3-O-methylglucose with little change in the Vmax.     

Glucose tolerance and insulin sensitivity following an one-week volleyball competition

The purpose of the study was to compare glucose tolerance and insulin sensitivity between trained (TR) and competition (CP) states, in relation to cortisol and testosterone levels. Sixteen highly trained volleyball players voluntarily participated in this study. The first testing session (TR state) occurred 1 week before the start of national level volleyball CP, and the second testing session (CP state) occurred next morning after the 1-week CP. Fasted serum sample was used for measuring cortisol and testosterone. Subjects were then orally challenged with 75 g of glucose solution for determinations of oral glucose tolerance test (OGTT) and insulin response. Under both fasted and glucose challenged conditions, glucose levels of CP were not different from TR state, whereas insulin levels of CP were significantly elevated above TR (50 min: from 78.8 +/- 8.7 to 96.6 +/- 8.1 microU/ml, P < 0.05; 80 min: from 62.8 +/- 7.0 to 82.0 +/- 7.3; P < 0.05). Muscle creatine kinase (CK) level in blood was significantly increased above TR, suggesting greater muscle damage by CP. Serum leptin level, percent fat mass, and body weight were not different between two states. CP significantly increased serum cortisol level without significantly change in testosterone level. The new finding of the study was that volleyball CP reduced the whole-body insulin sensitivity significantly compared to TR state. The greater level of insulin concentration under CP state appears to be associated with elevated serum cortisol level. Despites the benefit of increased physical activity on metabolic function is widely recognized, physiological stress associated with CP can result in attenuation of systemic insulin sensitivity compared TR state.     

Glucose tolerance test in the Ainu

In an attempt to find out specific characteristics in carbohydrate metabolism in the Ainu, if any, glucose tolerance test was carried out. Between the Ainu and non-Ainu Japanese no differences were observed in the blood glucose, immunoreactive insulin and human growth hormone levels in the plasma after glucose load. Fasting levels of plasma FFA were significantly lower in the Ainu than in the Japanese. Changes in the FFA after glucose load were less in the Ainu, while the Japanese showed a marked rebound of the plasma FFA.

---

Zusammenfassung Der Glukosetoleranztest wurde bei 10 Ainu und 20 Japanern (Studenten) durchgeführt. Signifikante Unterschiede im Blutzucker, immunreaktiven Insulin und humanen Wachstumshormon im Plasma wurden nach der Glukosegabe nicht gefunden. Die Nüchternwerte der freien Fettsäuren waren in den Ainu signifikant tiefer als bei den Japanern. Die Aenderungen der freien Fettsäuren nach Glukose waren bei den Ainu geringer, während die Japaner einen ausgeprägten "rebound effect" aufwiesen.

---

Resume On a appliqué un test de tolérance à la glucose à 10 Aïnous et à 20 Japonais d'autres races (tous étudiants). On n'a pas décelé de différence significative après administration de glucose ni dans la teneur en sucre du sang, ni dans le taux d'insuline immunoréactive, ni dans les hormones humaines de croissance contenues dans le plasma. Les coefficients d'acides gras libres (FFA), après un jeûne ont été plus bas chez les Aïnous que chez les Japonais et cela de façon significative. La modification des acides gras libres après administration de glucose a été moins marquée chez les Aïnous alors que les Japonais présentaient un net "effet de rebondissement".

     

Poplar metal tolerance protein 1 confers zinc tolerance and is an oligomeric vacuolar zinc transporter with an essential leucine zipper motif

Cation diffusion facilitator (CDF) proteins are a recently discovered family of cation efflux transporters that might play an essential role in metal homeostasis and tolerance. Here, we describe the identification, characterization, and localization of PtdMTP1, a member of the CDF family from the hybrid poplar Populus trichocarpa x Populus deltoides. PtdMTP1 is expressed constitutively and ubiquitously, although at low levels. Heterologous expression in yeast showed that PtdMTP1 was able to complement the hypersensitivity of mutant strains to Zn but not to other metals, including Cd, Co, Mn, and Ni. PtdMTP1 fused to green fluorescent protein localized to the vacuolar membrane both in yeast and in plant cells, consistent with a function of PtdMTP1 in zinc sequestration. Overexpression of PtdMTP1 in Arabidopsis confers Zn tolerance. We show that PtdMTP1, when expressed in yeast and Arabidopsis, forms homooligomers, a novel feature of CDF members. Oligomer formation is disrupted by reducing agents, indicating possible disulfide bridge formation. PtdMTP1 also contains a conserved Leu zipper motif. Although not necessary for oligomer formation, Leu residues within this motif are required for PtdMTP1 functional activity.