Quadriceps and Respiratory Muscle Fatigue Following High-Intensity Cycling in COPD Patients

Exercise intolerance in COPD seems to combine abnormal ventilatory mechanics, impaired O₂ transport and skeletal muscle dysfunction. However their relatie contribution and their influence on symptoms reported by patients remain to be clarified. In order to clarify the complex interaction between ventilatory and neuromuscular exercise limiting factors and symptoms, we evaluated respiratory muscles and quadriceps contractile fatigue, dynamic hyperinflation and symptoms induced by exhaustive high-intensity cycling in COPD patients. Fifteen gold II-III COPD patients (age = 67±6 yr; BMI = 26.6±4.2 kg.m^-2) performed constant-load cycling test at 80% of their peak workload until exhaustion (9.3±2.4 min). Before exercise and at exhaustion, potentiated twitch quadriceps strength (Q_tw), transdiaphragmatic (P_di,tw) and gastric (P_ga,tw) pressures were evoked by femoral nerve, cervical and thoracic magnetic stimulation, respectively. Changes in operational lung volumes during exercise were assessed via repetitive inspiratory capacity (IC) measurements. Dyspnoea and leg discomfort were measured on visual analog scale. At exhaustion, Q_tw (-33±15%, >15% reduction observed in all patients but two) and P_di,tw (-20±15%, >15% reduction in 6 patients) were significantly reduced (P<0.05) but not P_ga,tw (-6±10%, >15% reduction in 3 patients). Percentage reduction in Q_tw correlated with the percentage reduction in P_di,tw (r=0.66; P<0.05). Percentage reductions in P_di,tw and P_ga,tw negatively correlated with the reduction in IC at exhaustion (r=-0.56 and r=-0.62, respectively; P<0.05). Neither dyspnea nor leg discomfort correlated with the amount of muscle fatigue. In conclusion, high-intensity exercise induces quadriceps, diaphragm and less frequently abdominal contractile fatigue in this group of COPD patients. In addition, the rise in end-expiratory lung volume and diaphragm flattening associated with dynamic hyperinflation in COPD might limit the development of abdominal and diaphragm muscle fatigue. This study underlines that both respiratory and quadriceps fatigue should be considered to understand the complex interplay of factors leading to exercise intolerance in COPD patients.     

Antigenic relatedness between phospholipases A2 from Naja naja venom and from mammalian cells

Polyclonal antiserum was prepared against phospholipase A2 from Naja naja and used to prepare a purified antibody. It cross-reacted with the antigen, and with intracellular mammalian PLA2. This antibody was immunoreactive and inhibited the PLA2 activity of Naja naja and of guinea pig alveolar macrophages or rat lymphocytes. By immunoblotting, this antiserum revealed one band of PLA2 from Naja naja (14 kDa) and 3 bands for guinea pig alveolar macrophages and rat lymphocytes (30, 45 kDa and a minor band of 14 kDa). These results show an antigenic relatedness between an extracellular PLA2 and membrane-bound PLA2 from two different mammalian species and cell types.     

Molecular systematics and paleobiogeography of the South American sigmodontine rodents [published erratum appears in Mol Biol Evol 1998 Feb;15(2):224]

The murid rodent subfamily Sigmodontinae contains 79 genera which are distributed throughout the New World. The time of arrival of the first sigmodontines in South America and the estimated divergence time(s) of the different lineages of South American sigmodontines have been controversial due to the lack of a good fossil record and the immense number of extant species. The "early-arrival hypothesis" states that the sigmodontines must have arrived in South America no later than the early Miocene, at least 20 MYA, in order to account for their vast present-day diversity, whereas the "late-arrival hypothesis" includes the sigmodontines as part of the Plio-Pleistocene Great American Interchange, which occurred approximately 3.5 MYA. The phylogenetic relationships among 33 of these genera were reconstructed using mitochondrial DNA (mtDNA) sequence data from the ND3, ND4L, arginine tRNA, and ND4 genes, which we show to be evolving at the same rate. A molecular clock was calibrated for these genes using published fossil dates, and the genetic distances were estimated from the DNA sequences in this study. The molecular clock was used to estimate the dates of the South American sigmodontine origin and the main sigmodontine radiation in order to evaluate the "early-" and "late-arrival" scenarios. We estimate the time of the sigmodontine invasion of South America as between approximately 5 and 9 MYA, supporting neither of the scenarios but suggesting two possible models in which the invading lineage was either (1) ancestral to the oryzomyines, akodonts, and phyllotines or (2) ancestral to the akodonts and phyllotines and accompanied by the oryzomyines. The sigmodontine invasion of South America provides an example of the advantage afforded to a lineage by the fortuitous invasion of a previously unexploited habitat, in this case an entire continent.      

Does Auxin Binding Protein 1 Control Both Cell Division and Cell Expansion?

The Auxin-Binding Protein 1 (ABP1) was identified over 30 years ago thanks to it''s high affinity for active auxins. ABP1 plays an essential role in plant life yet to this day, its function remains ‘enigmatic.’ A recent study by our laboratory shows that ABP1 is critical for regulation of the cell cycle, acting both in G₁ and at the G₂/M transition. We showed that ABP1 is likely to mediate the permissive auxin signal for entry into the cell cycle. These data were obtained by studying a conditional functional knock-out of ABP1 generated by cellular immunization in the model tobacco cell line, Bright Yellow 2.Key Words: auxin responses, auxin-binding protein 1, immunomodulation, cellular immunisation     

[3H]thymidine incorporation in bovine lymphocytes treated with the tumor promoter, 12-O-tetradecanoyl phorobol-13-acetate

Treatment of bovine lymph node lymphocytes with the tumor promoter, 12-O-tetradecanoyl phorbol-13-acetate (TPA) leads to depressed [³H]thymidine incorporation in response to phytohemagglutinin (PHA). Radioautographic and morphological analyses showed that depression was at the level of blast-cell formation. Isotope-dilution experiments, and the use of [³H]deoxycytidine to label DNA indicated that the inhibition was not due to a block in thymidine transport in the treated cells. These experiments, as well as a bioassay designed to measure thymidine in the culture medium, showed that the apparent inhibition of [³H]thymidine incorporation and DNA synthesis was not the result of production of cold thymidine in the cultures. The results taken together support the idea that most TPA-treated cells are inhibited from responding to the mitogenic lectins. Those cells which do respond appear to form blast cells and synthesize DNA at the same rate as do untreated cells.     

The feeding, growth and behaviour of juvenile cod, Gadus morhua L., in cold environments

Most studies on feeding-related activities of fish in cold water (0° C) have not used eurythermal species or examined a broad suite of activities. In this study we report on the feeding, growth, behaviour and conversion-efficiency of 0 + Atlantic cod in response to water temperature and food availability. In one experiment, activity, opercular beat and growth decreased with decreasing temperature over the range 8·3–0·6° C. However, the conversion efficiency increased with decreasing temperature, a result partly explained by the relative change in activity and opercular rate. In another experiment, temperature had a linear effect on growth in cod fed different food rations. Both food availability and temperature were found to influence growth in group 0 + cod. The specific growth rate of cod in this experiment exceeded 2% day^-1. Growth data collected from cod sampled in the field during the cold-water period showed a progressive increase of mean length over the season. Overall, these results demonstrate that 0 + cod have adapted to life in cold-water environments, in contrast to adult cod which mostly inhabit warmer environments.