The application of 2H2O to measure skeletal muscle protein synthesis

Heath G Gasier,James D Fluckey,Stephen F Previs

doi:10.1186/1743-7075-7-31

Abstract

Skeletal muscle protein synthesis has generally been determined by the precursor:product labeling approach using labeled amino acids (e.g., [13C]leucine or [13C]-, [15N]-, or [2H]phenylalanine) as the tracers. Although reliable for determining rates of protein synthesis, this methodological approach requires experiments to be conducted in a controlled environment, and as a result, has limited our understanding of muscle protein renewal under free-living conditions over extended periods of time (i.e., integrative/cumulative assessments). An alternative tracer, 2H2O, has been successfully used to measure rates of muscle protein synthesis in mice, rats, fish and humans. Moreover, perturbations such as feeding and exercise have been included in these measurements without exclusion of common environmental and biological factors. In this review, we discuss the principle behind using 2H2O to measure muscle protein synthesis and highlight recent investigations that have examined the effects of feeding and exercise. The framework provided in this review should assist muscle biologists in designing experiments that advance our understanding of conditions in which anabolism is altered (e.g., exercise, feeding, growth, debilitating and metabolic pathologies).

Highlights

Skeletal muscle comprises ~40-45% of the total mass and ~60% of the total body protein in humans [1]; it is no surprise that skeletal muscle accounts for ~30-45% of whole body protein metabolism [2]
This is accomplished by examining changes that occur in gene expression, transcription factors and signal transduction pathways; the structure and function of skeletal muscle may largely be dependent on the renewal of protein
The flooding dose [7] can minimize labeling gradients by saturating the uptake of the amino acid by a tissue(s), questions such as whether muscle protein synthesis is stimulated when flooding with specific amino acid tracers [8,9] exists when conducting the experiment in the fasted state

Summary

Introduction

Skeletal muscle comprises ~40-45% of the total mass and ~60% of the total body protein in humans [1]; it is no surprise that skeletal muscle accounts for ~30-45% (dependent upon feeding and/or activity) of whole body protein metabolism [2]. In the second experiment [34], the rationale was to examine the effects of acute fasting (20 h) vs chronic food restriction (7 days) on FSR in rats In both designs, the FSR measurements were made over 5-6 h with feeding, since there is minimal concern for labeling gradients when using 2H2O, data were obtained with a certain degree of confidence. The FSR measurements were made over 5-6 h with feeding, since there is minimal concern for labeling gradients when using 2H2O, data were obtained with a certain degree of confidence Both studies provided new insight into two feeding extremes: 1) diet induced obesity results in an attenuation in the feeding induced stimulation of muscle protein synthesis in mice, and 2) both acute fasting and chronic food restriction significantly reduce muscle protein synthesis in rats.

Objective

Conclusions

Wagenmakers AJ

Findings

10. Ussing HH