Stable Isotope Tracers Applied to Measuring Rates of Protein Synthesis and Breakdown in Muscle: Principles and Applications
Year: 2011
Type: article
Abstract: Muscle is in a constant state of turnover, meaning that it is continuously synthesized and broken down. The balance between the rates of synthesis and breakdown determines if an individual is gaining or loosing muscle mass. It is therefore of interest in a variety of physiological circumstances to quantify the rates of muscle protein synthesis and breakdown. Tracer methodology using both radioactive and stable isotopes has been used in a wide variety of kinetic studies, including measurement of synthetic and breakdown rates of various compounds. Stable isotopes are particularly suited for the study of muscle protein metabolism, as multiple amino acid tracers can be used simultaneously, and multiple labels can be used with any individual amino acid, including labeling the nitrogen with 15N. Two basic approaches can be used to measure muscle protein synthesis. The direct incorporation of a labeled amino acid is the most conventional. This technique involves infusion or injection of tracer and measurement of subsequent incorporation into muscle protein over time. The measurement of the precursor enrichment, which is usually taken to be the free intracellular pool of the tracer amino acid, is necessary to calculate the actual rate of synthesis. Alternatively, the rate of muscle protein synthesis can be derived from the rate of uptake of an amino acid from blood. In this case incorporation of the amino acid into protein must be its only metabolic fate within the muscle. The basic principle of measuring muscle protein breakdown is to determine the rate at which intracellular amino acid tracer is diluted by the appearance of unlabeled amino acid that is not coming from the plasma. There are different approaches to accomplishing this measurement, and the choice of the optimal depends of the method used to measure protein synthesis. Ideally, methods to measure synthesis and breakdown are compatible (i.e., the same units) to enable calculation of the balance between synthesis and breakdown to determine if there is a net gain or loss in muscle protein.
Source: Europe PMC (PubMed Central)
Author: Robert R. Wolfe
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W10223380