Possible role for cell-surface carbohydrate-binding molecules in lymphocyte recirculation.

We are investigating the hypothesis that carbohydrate-binding molecules on the cell surface are involved in the recirculation of lymphocytes from the bloodstream into lymphoid organs. This phenomenon requires the specific attachment of circulating lymphocytes to the endothelial cells of postcapillary venules. Using an in vitro assay to measure the adhesive interaction between lymphocytes and postcapillary venules, we have found that L-fucose, D mannose, and the L-fucose-rich, sulfated polysaccharide fucoidin specifically inhibit this binding interaction. L-fucose shows stereo-selective inhibitory activity at concentrations greater than 18 mM while fucoidin produces 50% inhibition at approximately 1-5 X 10(-8) M. Fucoidin appears to interact with the lymphocyte, and not the postcapillary venule, to inhibit binding. These data suggest that cell surface carbohydrates (fucoselike) and carbohydrate-binding molecules (cell surface lectins) may contribute to the specific attachment of lymphocytes to postcapillary venules

Effect of expiratory muscle fatigue on exercise tolerance and locomotor muscle fatigue in healthy humans

High-intensity exercise (> or =90% of maximal O(2) uptake) sustained to the limit of tolerance elicits expiratory muscle fatigue (EMF). We asked whether prior EMF affects subsequent exercise tolerance. Eight male subjects (means +/- SD; maximal O(2) uptake = 53.5 +/- 5.2 ml.kg(-1).min(-1)) cycled at 90% of peak power output to the limit of tolerance with (EMF-EX) and without (CON-EX) prior induction of EMF and for a time equal to that achieved in EMF-EX but without prior induction of EMF (ISO-EX). To induce EMF, subjects breathed against an expiratory flow resistor until task failure (15 breaths/min, 0.7 expiratory duty cycle, 40% of maximal expiratory gastric pressure). Fatigue of abdominal and quadriceps muscles was assessed by measuring the reduction relative to prior baseline values in magnetically evoked gastric twitch pressure (Pga(tw)) and quadriceps twitch force (Q(tw)), respectively. The reduction in Pga(tw) was not different after resistive breathing vs. after CON-EX (-27 +/- 5 vs. -26 +/- 6%; P = 0.127). Exercise time was reduced by 33 +/- 10% in EMF-EX vs. CON-EX (6.85 +/- 2.88 vs. 9.90 +/- 2.94 min; P < 0.001). Exercise-induced abdominal and quadriceps muscle fatigue was greater after EMF-EX than after ISO-EX (-28 +/- 9 vs. -12 +/- 5% for Pga(tw), P = 0.001; -28 +/- 7 vs. -14 +/- 6% for Q(tw), P = 0.015). Perceptual ratings of dyspnea and leg discomfort (Borg CR10) were higher at 1 and 3 min and at end exercise during EMF-EX vs. during ISO-EX (P < 0.05). Percent changes in limb fatigue and leg discomfort (EMF-EX vs. ISO-EX) correlated significantly with the change in exercise time. We propose that EMF impaired subsequent exercise tolerance primarily through an increased severity of limb locomotor muscle fatigue and a heightened perception of leg discomfort

Editorial for special issue on education and humour: Education and humour as tools for social awareness and critical consciousness in contemporary classrooms

It is not new to consider the instructive power of humour. Both Plato and Aristotle, through their superiority theories, saw the benefit of wit as a social corrective, although they remained suspicious of the uneducated laughter of the masses (Plato in Morreall 1987; Aristotle in Morreall 1987). This approach has informed traditions of satire and resistance humour in a myriad of contexts. Stott summarises the raison d'être of satire through its aim “to denounce folly and vice and urge ethical and political reform through the subjection of ideas to humorous analysis” (Stott 2005: 109). The political potential of humour is easily recognised as a rhetorical and communicative device, yet it seems odd that little stock has been placed academically or culturally in the idea of humour as an educative tool in other social and cultural contexts and, more specifically, in the classroom

Phosphomannosyl receptors may participate in the adhesive interaction between lymphocytes and high endothelial venules.

Normal and malignant lymphocytes can migrate from the bloodstream into lymph nodes and Peyer's patches. This process helps distribute normal lymphocytes throughout the lymphoid system and may provide a portal of entry for circulating malignant cells. An adhesive interaction between lymphocytes and the endothelium of postcapillary venules is the first step in the migratory process. We have recently shown that the simple sugars L-fucose and D-mannose, and an L-fucose-rich polysaccharide (fucoidin), can inhibit this adhesive interaction in vitro. We now report that mannose-6-phosphate, the structurally related sugar fructose-1-phosphate, and a phosphomannan, core polysaccharide from the yeast Hansenula holstii (PPME) are also potent inhibitors. Inhibitory activity was assessed by incubating freshly prepared suspensions of lymphocytes, containing the various additives, over air-dried, frozen sections of syngeneic lymph nodes at 7-10 degrees C. Sections were then evaluated in the light microscope for the binding of lymphocytes to postcapillary venules. Mannose-6-phosphate and fructose-1-phosphate were potent inhibitors of lymphocyte attachment (one-half maximal inhibition at 2-3 mM). Mannose-1-phosphate and fructose-6-phosphate had slight inhibitory activity, while glucose-1-phosphate, glucose-6-phosphate, galactose-1-phosphate, and galactose-6-phosphate had no significant activity (at 10 mM). In addition, the phosphomannan core polysaccharide was a potent inhibitor (one-half maximal inhibition at 10-20 micrograms/ml); dephosphorylation with alkaline phosphatase resulted in loss of its inhibitory activity. Preincubation of the lymphocytes, but not the lymph node frozen sections, with PPME resulted in persistent inhibition of binding. Neither the monosaccharides nor the polysaccharide suppressed protein synthesis nor decreased the viability of the lymphocytes. Furthermore, inhibitory activity did not correlate with an increase in negative charge on the lymphocyte surface (as measured by cellular electrophoresis). These data suggest that a carbohydrate-binding molecule on the lymphocyte surface, with specificity for mannose-phosphates and structurally related carbohydrates, may be involved in the adhesive interaction mediating lymphocyte recirculation

Effects of oral creatine supplementation on high intensity, intermittent exercise performance in competitive squash players

The purpose of this study was to determine the effects of oral creatine supplementation on high intensity, intermittent exercise performance in competitive squash players. Nine squash players (mean ± SEM V˙O2max = 61.9 ± 2.1ml · kg-1 · min-1; body mass = 73 ± 3 kg) performed an on-court “ghosting” routine that involved 10 sets of 2 repetitions of simulated positional play, each set interspersed with 30 s passive recovery. A double blind, crossover design was utilised whereby experimental and control groups supplemented 4 times daily for 5 d with 0.075 g · kg-1 body mass of creatine monohydrate and maltodextrine, respectively, and a 4 wk washout period separated the crossover of treatments. The experimental group improved mean set sprint time by 3.2 ± 0.8 % over and above the changes noted for the control group (P = 0.004 and 95 % Cl = 1.4 to 5.1 %). Sets 2 to 10 were completed in a significantly shorter time following creatine supplementation compared to the placebo condition (P < 0.05). In conclusion, these data support existing evidence that creatine supplementation improves high intensity, intermittent exercise performance. In addition, the present study provides new evidence that oral creatine supplementation improves exercise performance in competitive squash players