Changes in muscle proton transverse relaxation times and acidosis during exercise and recovery

We studied changes in muscle proton ( 1H) transverse relaxation times (T 2) by magnetic resonance imaging during exercise and compared these changes with alterations in muscle metabolism measured by phosphorus-31 magnetic resonance spectroscopy ( 31P-MRS). Eleven subjects completed two trials of intermittent incremental forearm wrist flexion exercise requiring 30 contractions/min for 5 min, 7 min of recovery between stages, and 5-N load increments/stage. Between stages of the first trial, T 2 images of muscle 1H were obtained. Muscle T 2 increased from 27.3 ± 1.1 (SD) ms at rest to 35.8 ± 3.6 ms after volitional fatigue (P < 0.05), whereas less active wrist extensor muscle T 2 remained unchanged (26.8 ± 0.9 to 28.8 ± 1.6 ms; P > 0.05). After localizing the predominant muscle recruited from the T 2 images, subjects completed an identical trial at least 1 wk later but involving surface coil 31P-MRS of the T 2-enhanced muscle to measure the H + concentration ([H +]). Intramuscular [H +] of T 2-enhancing muscle increased from 1.1 ± 0.1 x 10 -7 M at rest to 4.1 ± 2.0 x 10 -7 M after volitional fatigue. Both muscle T 2 and intramuscular [H +] increased in a bimodal manner, with T 2 increasing before muscle [H +] (P < 0.05). The correlation coefficient between the percent change in T 2 and muscle [H +] during exercise was +0.74 (range 0.48-0.98; P < 0.05) and +0.47 during recovery. After 12 min of recovery, muscle [H +] decreased to 1.4 ± 0.3 x 10 -7 M (P < 0.05), and T 2 remained close to postexercise values (32.2 ± 3.1 ms, P > 0.05). The data indicate that 1) the T 2 increases during increases in exercise intensity are nonlinear, 2) the T 2 increases during exercise are significantly correlated with increases in [H +], and 3) the slow recovery of T 2 compared with [H +] indicates that [H +] has a minor contribution to the recovery in T 2

The genetic drift of human papillomavirus type 16 is a means of reconstructing prehistoric viral spread and the movement of ancient human populations

Journal of Virology67116413-6423JOVI

Characterization of a novel coronavirus associated with severe acute respiratory syndrome

In March 2003, a novel coronavirus (SARS-CoV) was discovered in association with cases of severe acute respiratory syndrome (SARS). The sequence of the complete genome of SARS-CoV was determined, and the initial characterization of the viral genome is presented in this report. The genome of SARS-CoV is 29,727 nucleotides in length and has 11 open reading frames, and its genome organization is similar to that of other coronaviruses. Phylogenetic analyses and sequence comparisons showed that SARS-CoV is not closely related to any of the previously characterized coronaviruses