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Intracellular acidification and volume increases explain R 2 decreases in exercising muscle
Author(s) -
Damon Bruce M.,
Gregory Carl D.,
Hall Kristen L.,
Stark Heather J.,
Gulani Vikas,
Dawson M. Joan
Publication year - 2002
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.10043
Subject(s) - intracellular , intracellular ph , chemistry , osmolyte , oxidative phosphorylation , glycolysis , anaerobic exercise , biophysics , metabolism , medicine , endocrinology , biochemistry , biology , physiology
Exercise‐induced decreases in the 1 H transverse relaxation rate ( R 2 ) of muscle have been well documented, but the mechanism remains unclear. In this study, the hypothesis was tested that R 2 decreases could be explained by pH decreases and apparent intracellular volume (V i ′) increases. 31 P and 1 H spectroscopy, biexponential R 2 analysis, and imaging were performed prior to and following fatiguing exercise in iodoacetate‐treated (IAA, to inhibit glycolysis), NaCN‐treated (to inhibit oxidative phosphorylation), and untreated frog gastrocnemii. In all exercised muscles, the apparent intracellular R 2 ( R 2i ′) and pH decreased, while intracellular osmolytes and V i ′ increased. These effects were larger in NaCN‐treated and untreated muscles than in IAA‐treated muscles. Multiple regression analysis showed that pH and V i ′ changes explain 70% of the R 2i ′ variance. Separate experiments in unexercised muscles demonstrated causal relationships between pH and R 2i ′ and between V i ′ and R 2i ′. These data indicate that the R 2 change of exercise is primarily an intracellular phenomenon caused by the accumulation of the end‐products of anaerobic metabolism. In the NaCN‐treated and untreated muscles, the R 2i ′ change increased as field strength increased, suggesting a role for pH‐modulated chemical exchange. Magn Reson Med 47:14–23, 2002. © 2002 Wiley‐Liss, Inc.