The diversity of (13)C isotope discrimination in a Quercus robur full-sib family is associated with differences in intrinsic water use efficiency, transpiration efficiency, and stomatal conductance.

(13)C discrimination in organic matter with respect to atmospheric CO(2) (Delta(13)C) is under tight genetic control in many plant species, including the pedunculate oak (Quercus robur L.) full-sib progeny used in this study. Delta(13)C is expected to reflect intrinsic water use efficiency, but this assumption requires confirmation due to potential interferences with mesophyll conductance to CO(2), or post-photosynthetic discrimination. In order to dissect the observed Delta(13)C variability in this progeny, six genotypes that have previously been found to display extreme phenotypic values of Delta(13)C [either very high ('high Delta') or low ('low Delta') phenotype] were selected, and transpiration efficiency (TE; accumulated biomass/transpired water), net CO(2) assimilation rate (A), stomatal conductance for water vapour (g(s)), and intrinsic water use efficiency (W(i)=A/g(s)) were compared with Delta(13)C in bulk leaf matter, wood, and cellulose in wood. As expected, 'high Delta' displayed higher values of Delta(13)C not only in bulk leaf matter, but also in wood and cellulose. This confirmed the stability of the genotypic differences in Delta(13)C recorded earlier. 'High Delta' also displayed lower TE, lower W(i), and higher g(s). A small difference was detected in photosynthetic capacity but none in mesophyll conductance to CO(2). 'High Delta' and 'low Delta' displayed very similar leaf anatomy, except for higher stomatal density in 'high Delta'. Finally, diurnal courses of leaf gas exchange revealed a higher g(s) in 'high Delta' in the morning than in the afternoon when the difference decreased. The gene ERECTA, involved in the control of water use efficiency, leaf differentiation, and stomatal density, displayed higher expression levels in 'low Delta'. In this progeny, the variability of Delta(13)C correlated closely with that of W(i) and TE. Genetic differences of Delta(13)C and W(i) can be ascribed to differences in stomatal conductance and stomatal density but not in photosynthetic capacity.

New parameters reducing the interindividual variability of metabolic changes during muscle contraction in humans. A (31)P MRS study with physiological and clinical implications.

Interindividual variations in skeletal muscle metabolism make comparative analyses difficult. In this study, we have addressed the issue of capturing the variability of metabolic performance observed during muscle exercise in humans by using an original method of normalization.Metabolic changes induced by various kinds of exercise were investigated using 31P magnetic resonance spectroscopy (MRS) at 4.7 T in 65 normal subjects (23 women and 42 men) and 12 patients with biopsy-proven muscular disorders. Large variations in the extent of PCr breakdown and intracellular acidosis were recorded among subjects and exercise protocols. For all the data pooled, the amplitude of mechanical performance accounts for 50% of these variations. When scaled to the work output, variations of PCr consumption account for 65% of pH changes through a linear relationship. This linear relationship was substantially improved (90%) when both variables were scaled to the square of work output performed (P1 and P2). By capturing most of the initial interindividual variability (90%), P1 vs. P2 relationship represents an ideal standardization procedure, independent of any anthropometric measurements. This relationship also discloses a significant link between the extent of PCr breakdown and intracellular acidosis regardless of exercise protocol. Moreover, changes in the slope of the P1 vs. P2 regression curve, as measured in old subjects and in selected patients, directly reflect alterations of energy production in muscle.

Transmission of apoptosis in human colorectal tumor cells exposed to capecitabine, Xeloda, is mediated via Fas.

We developed an original in vitro model dedicated to the exploration of molecular pharmacology of the new oral fluoropyrimidine capecitabine (Xeloda). More specifically, in this report, we investigated whether apoptosis induced by capecitabine was mediated by the Fas/FasL system. To achieve this goal, a specific in vitro coculture model mixing hepatoma and human colorectal cell line was used. A bystander effect was observed between HepG2 and LS174T cells treated with capecitabine. Besides this, Xeloda showed a 7-fold higher cytotoxicity and markedly stronger apoptotic potential in thymidine phosphorylase (TP)-transfected LS174T-c2 cells. The striking enhancement of thymidylate synthase inhibition that we observed in cells with high TP activity was most probably at the origin of the potentiation of capecitabine antiproliferative efficacy. In addition, this increase of sensitivity was accompanied by a strong overexpression of the CD95-Fas receptor on the cell surface. Both Fas and FasL mRNA expression were triggered after exposing TP+ cells to the drug. This implication of Fas in Xeloda-induced apoptosis was next confirmed by using antagonistic anti-Fas and anti-FasL antibodies that proved to reverse capecitabine antiproliferative activity, thus highlighting the key role that Fas could play in the optimization of an antitumor response to fluoropyrimidine drugs. Our data, therefore, show that TP plays a key role in the capecitabine activity and that the Fas/FasL system could be considered as a new determinant for Xeloda efficacy.

ATP synthesis and proton handling in muscle during short periods of exercise and subsequent recovery.

We used (31)P-magnetic resonance spectroscopy to study proton buffering in finger flexor muscles of eight healthy men (25-45 yr), during brief (18-s) voluntary finger flexion exercise (0.67-Hz contraction at 10% maximum voluntary contraction; 50/50 duty cycle) and 180-s recovery. Phosphocreatine (PCr) concentration fell 19 +/- 2% during exercise and then recovered with half time = 0.24 +/- 0.01 min. Cell pH rose by 0.058 +/- 0.003 units during exercise as a result of H(+) consumption by PCr splitting, which (assuming no lactate production or H(+) efflux) implies a plausible non-P(i) buffer capacity of 20 +/- 3 mmol. l intracellular water(-1). pH unit(-1). There was thus no evidence of significant glycogenolysis to lactate during exercise. Analysis of PCr kinetics as a classic linear response suggests that oxidative ATP synthesis reached 48 +/- 2% of ATP demand by the end of exercise; the rest was met by PCr splitting. Postexercise pH recovery was faster than predicted, suggesting "excess proton" production, with a peak value of 0.6 +/- 0.2 mmol/l intracellular water at 0.45 min of recovery, which might be due to, e.g., proton influx driven by cellular alkalinization, or a small glycolytic contribution to PCr resynthesis in recovery.

Glucose and galactose regulate intestinal absorption of cholesterol.

A dose-dependent increase in cholesterol absorption was induced by glucose addition (0-75 mM) to the apical medium of TC7 cells, a well-characterized clone of Caco-2. The uptake into the cells and the secretion rate to the basolateral space were both enhanced by glucose and galactose. This up-regulation was suppressed by SGLT1 inhibition but not by GLUT2 inhibition. Cholesterol cell uptake was significantly decreased by PMA and increased by chelerythrine, with more pronounced changes in the presence of hexoses. Thus, the involvement of a protein kinase C signalling pathway was evidenced in the regulation processes of intestinal cholesterol absorption. In the presence of antibodies directed to hSR-BI cholesterol absorption was reduced by 40% and glucose or galactose no longer enhanced it. We suggest that glucose or galactose, through an interaction with SGLT1, activates a protein kinase C pathway that regulates the activity of one of the intestinal cholesterol transporters, namely hSR-BI.