Rat skeletal muscle triacylglycerol utilization during exhaustive swimming

The utilization of triacylglycerol in slow oxidative, fast oxidative-glycolytic, and fast glycolytic skeletal muscle fiber types was examined in rats subjected to a prolonged exhaustive swim. Significant reductions of intramuscular triacylglycerol occurred following 2 h and 40 min of swimming in all muscles containing a predominance of slow oxidative and fast oxidative-glycolytic fibers, which possess a high capacity for free fatty acid oxidation. Triacylglycerol content in the soleus decreased by 48%, and reductions of 41, 29, and 27% were measured in the red vastus lateralis, red gastrocnemius, and plantaris muscles, respectively. In the white vastus lateralis and white gastrocnemius muscles (fast glycolytic fibers) triacylglycerol concentrations were unaffected. In all muscles the variability of intramuscular triacylglycerol measurements between animals was 20-50% and the within animal variance (right vs. left hindlimb) was similar. Analytical repeatability was approximately 10% in all muscles and significantly less than the between- and within-animal variances. It was concluded that a real biological variation exists in the triacylglycerol content of all rat skeletal muscles and that intramuscular triacylglycerol is an important energy source during prolonged exercise of moderate intensity.     

Statistical properties of the variation at linked microsatellite loci: implications for the history of human Y chromosomes [published erratum appears in Mol Biol Evol 1997 Mar;14(3):354]

It has recently been suggested that observed levels of variation at microsatellite loci can be used to infer patterns of selection in genomes and to assess demographic history. In order to evaluate the feasibility of these suggestions it is necessary to know something about how levels of variation at microsatellite loci are expected to fluctuate due simply to stochasticity in the processes of mutation and inheritance (genetic sampling). Here we use recently derived properties of the stepwise mutation model to place confidence intervals around the variance in repeat score that is expected at mutation-drift equilibrium and outline a statistical test for whether an observed value differs significantly from expectation. We also develop confidence intervals for the time course of the buildup of variation following a complete elimination of variation, such as might be caused by a selective sweep or an extreme population bottleneck. We apply these methods to the variation observed at human Y-specific microsatellites. Although a number of authors have suggested the possibility of a very recent sweep, our analyses suggest that a sweep or extreme bottleneck is unlikely to have occurred anytime during the last approximately 74,000 years. To generate this result we use a recently estimated mutation rate for microsatellite loci of 5.6 x 10(-4) along with the variation observed at autosomal microsatellite loci to estimate the human effective population size. This estimate is 18,000, implying an effective number of 4,500 Y chromosomes. One important general conclusion to emerge from this study is that in order to reject mutation-drift equilibrium at a set of linked microsatellite loci it is necessary to have an unreasonably large number of loci unless the observed variance is far below that expected at mutation-drift equilibrium.      

Energy cost and metabolic regulation during intermittent and continuous tetanic contractions in human skeletal muscle

Muscle ATP turnover, glycogenolytic, and glycolytic rates were estimated to compare the energy cost and glycolytic regulation of 102.4 s of continuous and intermittent stimulation. Quadriceps femoris muscles of male subjects were stimulated at 20 Hz for one continuous contraction (n = 6) or a series of 64 contractions (1.6 s on, 1.6 s off; n = 6). Leg blood flow was occluded and muscle biopsies were obtained at rest and following 51.2 and 102.4 s of contraction time in both conditions. Isometric force production by the activated knee extensors decreased to 55% of initial contraction force with intermittent and 80% of initial contraction force with continuous stimulation following 51.2 s of contraction time. Corresponding ATP turnover rates were 4.49 +/- 0.39 and 3.80 +/- 0.44 mmol.kg dry muscle-1.s-1. When normalized for tension production the respective energy costs of intermittent and continuous contractions were 3.66 +/- 0.47 and 2.64 +/- 0.36 mmol ATP.kg-1.100 N-1. Glycogenolytic rates were identical during the first 51.2 s of stimulation but glycolysis was higher in the intermittent group (1.05 +/- 0.10 vs. 0.86 +/- 0.11 mmol.kg-1.s-1). We suggest that the increased ATP utilization of intermittent contractions is associated with enhanced Ca2+-transport ATPase activity during relaxation and enhanced actomyosin ATPase activity during the early portion of each contraction. Glycolytic rate is dependent on ATP demand and regulated by allosteric modulators of phosphofructokinase and pyruvate kinase which are released or consumed in the reactions associated with contraction.     

MetaTM - a consensus method for transmembrane protein topology prediction

Background  

Transmembrane (TM) proteins are proteins that span a biological membrane one or more times. As their 3-D structures are hard to determine, experiments focus on identifying their topology (i. e. which parts of the amino acid sequence are buried in the membrane and which are located on either side of the membrane), but only a few topologies are known. Consequently, various computational TM topology predictors have been developed, but their accuracies are far from perfect. The prediction quality can be improved by applying a consensus approach, which combines results of several predictors to yield a more reliable result.