Measuring the kinetics of biomolecular recognition with magnetic colloids.

We introduce a general methodology based on magnetic colloids to study the recognition kinetics of tethered biomolecules. Access to the full kinetics of the reaction is provided by an explicit measure of the time evolution of the reactant densities. Binding between a single ligand and its complementary receptor is here limited by the colloidal rotational diffusion. It occurs within a binding distance that can be extracted by a reaction-diffusion theory that properly accounts for the rotational Brownian dynamics. Our reaction geometry allows us to probe a large diversity of bioadhesive molecules and tethers, thus providing a quantitative guidance for designing more efficient reactive biomimetic surfaces, as required for diagnostic, therapeutic, and tissue engineering techniques.

Acceleration of the recognition rate between grafted ligands and receptors with magnetic forces.

When ligands and receptors are both attached on surfaces, because of the restriction of configurational freedom, their recognition kinetics may be substantially reduced as compared with freely diffusing species. In nature, this reduction may influence the efficiency of the capture and adhesion of circulating cells. Here we show that similar consequences are observed for colloids grafted with biomolecules that are used as probes for diagnostics. We exploit Brownian magnetic colloids that self-assemble into linear chains to show also that the resulting one-dimensional confinement considerably accelerates the recognition rate between grafted receptors and their ligands. We propose that because confinement significantly augments the colliding frequency, it also causes a large increase in the attempt frequency of the recognition. This work gives the basis of a rapid, homogeneous, and highly sensitive bioanalysis method.

Flexible magnetic filaments as micromechanical sensors.

We propose a new micromechanical approach to probe bending rigidity at molecular scale. Long flexible filaments made of magnetic colloids and linkers are shown to adopt under magnetic field a hairpin configuration. Measuring the hairpin curvature as a function of the field intensity and the linker length from diffracted light allows us to deduce the linker bending rigidity kappa. The technique is presented for two types of linkers: a spontaneously adsorbing polymer and a grafted biomolecular.

Effects of inhaled salbutamol in exercising non-asthmatic athletes.

BACKGROUND: Beta-2 agonists such as salbutamol are used, not only by asthmatic athletes to prevent exercise induced asthma, but also by non-asthmatic athletes as a potentially ergogenic agent. We have investigated whether inhaled salbutamol enhances endurance performance in non-asthmatic athletes. METHODS: A prospective double blind, randomised, three way crossover design was used to study the effects of 200 microg and 800 microg inhaled salbutamol versus a placebo in 12 trained triathletes. The treatments were compared in three identical cycle ergometer sessions at 85% of the predetermined maximal oxygen uptake. Lung function, endurance time, metabolic parameters (glucose, potassium, lactate, free fatty acid, and glycerol), and psychomotor performance were evaluated. RESULTS: Neither endurance time nor post-exercise bronchodilation were significantly different between the treatments. Metabolic parameters were affected by exercise but not by treatment. CONCLUSIONS: Inhaled salbutamol, even in a high dose, did not have a significant effect on endurance performance in non-asthmatic athletes, although the bronchodilating effect of the drug at the beginning of exercise may have improved respiratory adaptation. Our results do not preclude an ergogenic effect of beta2 agonists given by other routes or for a longer period.

Single and choice reaction time during prolonged exercise in trained subjects: influence of carbohydrate availability.

The aim of the present study was to examine the effects of prolonged exercise at the ventilatory threshold and carbohydrate ingestion on single (SRT) and choice (CRT) reaction time. Eight well-trained triathletes completed three testing sessions within a 3-week period. Maximal oxygen uptake was determined in the first test, whereas the second and the third sessions were composed of a 100-min run (treadmill 15 min, overground 70 min, treadmill 15 min) performed at the velocity associated with the ventilatory threshold. During these submaximal tests, the subjects ingested (in random order) 8 ml x kg(-1) body weight of either a placebo (Pl) or 5.5% carbohydrate (CHO) solution prior to the first submaximal run and 2 ml x kg(-1) body weight every 15 min after that. The cognitive tasks were performed before and after exercise for CRT, and before, during each submaximal run and after exercise for SRT. Furthermore, at the end of each submaximal test subjects were asked to report their rating of perceived exertion (RPE). Results showed a significant positive effect of CHO ingestion on RPE and CRT performance at the end of exercise, while no effect of exercise duration was found in the Pl condition. After a 100-min run, during the CHO condition, CRT mean (SD) group values decreased from 688.5 (51) ms to 654 (63) ms, while during the Pl condition, RPE mean group values increased from 11 (2) to 16 (1.02) and CRT mean values remained stable [688 (104) ms vs 676 (73.4) ms, P > 0.05]. No similar effect was observed for SRT. These results suggest that CHO-electrolyte ingestion during a 100-min run results in an improvement in the complex cognitive performance measured at the end of that run.

Carbohydrate ingestion does not influence the change in energy cost during a 2-h run in well-trained triathletes.

The aim of this study was to examine whether the increase in the energy cost of running (C(r)), previously reported to occur at the end of a prolonged run, could be influenced by the ingestion of either an artificially sweetened placebo (Pl) or a 5.5% carbohydrate (CHO) solution. Ten well-trained triathletes completed three testing sessions within a 3-week period. The aim of the first session was to determine maximal oxygen uptake (VO(2)(max)) and the velocity associated with ventilatory threshold (nu(VT)). The second and the third sessions were composed of two submaximal treadmill runs (20 min long, 0% grade, performed at nu(VT)), before and after an 80-min overground run, also conducted at nu(VT). During these submaximal tests, the subjects ingested (in a random order) either a Pl or CHO solution prior to the first submaximal run and every 20 min after that. During the first session, ventilatory threshold (VT) occurred at [mean (SD)] 81.2 (2.5)% VO(2)(max) and 16.5 (0.6) km. h(-1). A significant effect of exercise duration was found on C(r) (DeltaC(r)) at the end of the run, whatever the solution ingested (DeltaC(r) = 5.7% and 7.01% for CHO and Pl, respectively). A reduction in the respiratory exchange ratio (from 0.98 to 0.90) was observed only at the end of the Pl trial. In this study, C(r) seems to be affected only to a minor extent by substrate turnover. Moreover, the increase in the demand for oxygen, estimated from the increase in ventilation, accounted for only a minor proportion of the increase in C(r) (11% and 17% for CHO and Pl, respectively). No correlation was found between the changes in C(r) and the changes in the other physiological parameters recorded. These results suggest, indirectly, that C(r) increases during a 2-h run at 80% VO(2)(max) in well-trained subjects can be explained mainly by alterations in neuromuscular performance, which lead to a decrease in muscle efficiency.

[Continuous ambulatory enteral feeding in hospitalized adults: prospective experience in 98 patients]. / Nutrition entérale continue ambulatoire à l'hôpital, chez l'adulte: expérience prospective chez 98 malades.

The goal of this study, which describes a personal technique of continuous enteral nutrition (CEN) in hospitalized adults on an ambulatory basis, was: to prospectively evaluate, over a 2-year period, its efficacy and tolerance in 98 patients requiring CEN for at least 15 days; to compare its efficacy and tolerance with those of conventional non-ambulatory CEN on a prospectively randomized basis in 16 patients. Ambulatory CEN was given at the rate of 35-45 kcal/kg/d (lipids: 35 p. 100; carbohydrates: 45 p. 100); during day-time, a portable system, including pump, tubes and low-viscosity nutrient solutions, allowed ambulation. Ninety-eight consecutive patients with a minimal level of physical autonomy were treated for intestinal (n = 47), pancreatic (n = 20), esophagogastric (n = 17) diseases, or for malnutrition of other causes for an average of 38 days (15 to 141). The average weight gain (m +/- SD) was 1.2 +/- 5.5 p. 100 of ideal body weight (IBW) and the average nitrogen gain was 0.7 +/- 3.8 g/24 h; weight gain proved significantly lower in patients with inflammatory bowel disease receiving steroids. The clinical tolerance proved excellent, except for 5 cases of transient diarrhea and 9 cases of reposition of the nasogastric tube. A decrease in cholesterolemia below 3.9 mmol/l was noted in 25 p. 100 of patients during CEN. No significant difference between ambulatory and non-ambulatory CEN was observed in terms of evolution of body weight and other anthropometric variables, nitrogen balance, albuminemia, and oxygen consumption; conversely, the CEN experience, evaluated by patients on analogical visual scales, was significantly better endured in the ambulatory group.(ABSTRACT TRUNCATED AT 250 WORDS)