Functional torque-velocity and power-velocity characteristics of elite athletes

Technical limitations of some isokinetic dynamometers have called into question the validity of some data on human muscle mechanics. The Biodex dynamometer has been shown to minimize the impact artefact while permitting automatic gravity correction. This dynamometer was used to study quadriceps muscle torque and power generation in elite power (n = 6) and elite endurance (n = 7) athletes over 12 randomly assigned isokinetic velocities from 30 degrees.s-1 to 300 degrees.s-1. The angle at peak torque varied as a negative, linear function of angular velocity, with the average angle across test velocities being 59.5 degrees (SD 10.2 degrees). Power athletes developed greater peak torque at each angular velocity (P less than 0.05) and experienced a 39.7% decrement in torque over the velocity range tested. Endurance athletes encountered a 38.8% decline in peak torque. Torques measured at 60 degrees of knee flexion followed a similar trend in both groups; however the greatest torques were recorded at 60 degrees.s-1 rather than at 30 degrees.s-1. Leg extensor muscle power increased monotonically with angular velocity in both power (r2 = 0.728) and endurance athletes (r2 = 0.839); however these curves diverged significantly so that the power athletes produced progressively more power with each velocity increment. These inter group differences probably reflected a combination of natural selection and training adaptation.     

Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium

Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel.     

DNA sequence has an effect on the extent and kinds of alkylation of DNA by a potent carcinogen

A system has been developed to study the effects of base sequence (neighboring bases) upon the alkylation of guanine (G) and adenine (A) bases in DNA. The study was performed on the synthetic polydeoxyribonucleotides, poly(dG).poly(dC), poly(dG-dC).poly(dG-dC), poly(dA).poly(dT), poly(dA-dT).poly(dA-dT), poly(dA-dC).poly(dG-dT), poly(dA-dG).poly(dC-dT), as well as calf thymus DNA. Each polynucleotide was treated with N-[3H]methyl-N-nitrosourea (MNU), depurinated, and the freed alkylpurines separated by HPLC and quantitated by liquid scintillation counting. The amounts of 3-methylguanine (3-MG), 7-MG, and O6-MG relative to guanine, and 3-methyladenine (3-MA) and 1-MA plus 7-MA relative to adenine, and also the O6-MG/7-MG ratios were highly reproducible for a given polynucleotide. Significant differences were found in the amounts of each of the methylpurines formed when compared among the six synthetic polynucleotides and DNA. This evidence is interpreted as an effect upon alkylation which is ultimately dependent upon the base sequence. These findings may have significance in defining the specificity of chemical carcinogens in terms of the susceptability to modification of nucleotide sequences such as those found in certain oncogenes.     

Ultrastructural Changes During Germination of Dictyostelium discoideum Spores

Spores of Dictyostelium discoideum undergo significant changes in fine structure during germination. The mitochondria progressively become less dense and lose their peripherally attached ribosomes, and the tubuli become more pronounced as germination proceeds. During this period, the three-layered spore wall breaks down in two stages: first, the outer and middle layers are ruptured as a unit, and, second, the inner wall is breached. Crystals and dark (lipid) bodies disappear shortly before or during emergence of the myxamoebae. Autophagic vacuoles are found in dormant spores and throughout the entire germination process. The addition of cycloheximide to germinating spores inhibited the loss of the crystals and dark (lipid) bodies. In addition, the drug inhibited the breakdown of the inner wall layer. Cycloheximide did not prevent the formation of the water expulsion vesicle or the apparent function of the autophagic vacuoles.     

Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal

We have developed a new approach to the measurement of phylogenetic signal in character state matrices called relative apparent synapomorphy analysis (RASA). RASA provides a deterministic, statistical measure of natural cladistic hierarchy (phylogenetic signal) in character state matrices. The method works by determining whether a measure of the rate of increase of cladistic similarity among pairs of taxa as a function of phenetic similarity is greater than a null equiprobable rate of increase. Our investigation of the utility and limitations of RASA using simulated and bacteriophage T7 data sets indicates that the method has numerous advantages over existing measures of signal. A first advantage is computational efficiency. A second advantage is that RASA employs known methods of statistical inference, providing measurable sensitivity and power. The performance of RASA is examined under various conditions of branching evolution as the number of characters, character states per character, and mutations per branch length are varied. RASA appears to provide an unbiased and reliable measure of phylogenetic signal, and the general approach promises to be useful in the development of new techniques that should increase the rigor and reliability of phylogenetic estimates.      

RasG protein accumulation occurs just prior to amoebae emergence during spore germination in Dictyostelium discoideum

Abstract RasG protein levels in dormant and germinating spores of Dictyostelium discoideum strains JC1 and SG1 were estimated by Western blotting. Ras Glevels were very low in dormant spores and remained low during the lag period, regardless of whether spores were heat activated or treated with autoactivator during the early stages of spore germination. RasG levels increased late during spore swelling just prior to the emergence stage of germination. These data are consistent with a requirement for RasG during vegetative growth.     

Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis)

Analysis of the heat-shock proteins (hsps) of six closely related species of Poeciliopsis demonstrated the existence of biochemical diversity in the hsp100, hsp70, hsp60, and hsp30 protein families among species. Each species expressed five to seven hsp70-related isoforms. Constitutive 70-kD isoforms were identical among species, but four different patterns of heat-inducible isoforms were seen in these six species. Members of the hsp70 family of molecular chaperones are included among the most highly conserved proteins known, and the possibility of variation in hsp70 among closely related species has rarely been addressed. The hsp30 family is known to be less conserved than the hsp70 family, and, as expected, the Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30 isoforms characteristic of a particular species were unique to that species. Hsp100 and hsp60 were identical in five of the species, but alternate isoforms were found in P. monacha. The small size and limited geographical distribution of the P. monacha population have probably contributed to the uniqueness of the monacha pattern. Two of the species were shown to acquire thermotolerance, the ability to withstand normally lethal temperatures when subjected to a gradual temperature increase. Rapid-heating protocols commonly used to establish critical thermal maxima of organisms do not include this inducible component of thermoresistance and therefore do not adequately assess an organism's capacity to withstand thermal stress.