Measuring perfusion and bioenergetics simultaneously in mouse skeletal muscle: a multiparametric functional‐NMR approach

Abstract

A totally noninvasive set-up was developed for comprehensive NMR evaluation of mouse skeletal muscle function in vivo. Dynamic pulsed arterial spin labeling-NMRI perfusion and blood oxygenation level-dependent (BOLD) signal measurements were interleaved with (31)P NMRS to measure both vascular response and oxidative capacities during stimulated exercise and subsequent recovery. Force output was recorded with a dedicated ergometer. Twelve exercise bouts were performed. The perfusion, BOLD signal, pH and force-time integral were obtained from mouse legs for each exercise. All reached a steady state after the second exercise, justifying the pointwise summation of the last 10 exercises to compensate for the limited (31)P signal. In this way, a high temporal resolution of 2.5 s was achieved to provide a time constant for phosphocreatine (PCr) recovery (τ(PCr)). The higher signal-to-noise ratio improved the precision of τ(PCr) measurement [coefficient of variation (CV) = 16.5% vs CV = 49.2% for a single exercise at a resolution of 30 s]. Inter-animal summation confirmed that τ(PCr) was stable at steady state, but shorter (89.3 ± 8.6 s) than after the first exercise (148 s, p < 0.05). This novel experimental approach provides an assessment of muscle vascular response simultaneously to energetic function in vivo. Its pertinence was illustrated by observing the establishment of a metabolic steady state. This comprehensive tool offers new perspectives for the study of muscle pathology in mice models.

Combined MRI and 31P-MRS Investigations of the ACTA1(H40Y) Mouse Model of Nemaline Myopathy Show Impaired Muscle Function and Altered Energy Metabolism

“…Over the last decade, analysis of PCr recovery kinetics has been extensively used in order to investigate in vivo skeletal muscle mitochondrial oxidative capacity [41], [42]. Previous animal studies reported PCr recovery times typically ranging from ∼50 sec to ∼160 sec according to the end-of-exercise pH values [31], [41], [43]. From a methodological point of view, it should be pointed out that PCr recovery is usually fitted with a monoexponential function so that the temporal resolution of the raw dataset is of utmost importance for an accurate measurement of the corresponding variables.…”

Skeletal muscle ATP synthesis and cellular H+ handling measured by localized 31P-MRS during exercise and recovery

“…With repetition time T R  = 6 seconds, this resulted in an effective exercise frequency of 0.3 Hz. To minimize habituation effects28 and standardize exercise conditions, an equivalent preparatory exercise bout was executed 40 min before acquiring MRS data during exercise. The exercise bouts for acquiring data in GM and in SOL were separated by 28 minutes of rest on average (minimum was 20 min), to ensure that PCr, Pi and pH values were fully recovered to basal levels at the beginning of the second bout.…”

Skeletal muscle quantitative nuclear magnetic resonance imaging and spectroscopy as an outcome measure for clinical trials (part II)

“…Контраст BOLD (blood oxygen level dependent -зависимый уровень кислорода крови) [132], обладающий способностью обнаруживать акти-вацию мозга, позволяет определять оксигенацию ка-пиллярной и венозной крови в скелетных мышцах и полуколичественно оценивать насыщение крови кислородом [138,139]. В отличие от большинства слу-чаев применения контраста BOLD в исследованиях головного мозга, результат анализа скелетных мышц может быть отрицательным при глубокой кислородной десатурации (падение степени насыщения крови кис-лородом) и положительным, когда выделение тканями кислорода уменьшается [140][141][142][143][144]. Общий и капил-лярный объемы крови влияют на сигнал от контраста BOLD, что осложняет интерпретацию результатов [145].…”