| 11754438 |
Damon BM, Gregory CD, Hall KL, Stark HJ, Gulani V, Dawson MJ: Intracellular acidification and volume increases explain R (2) decreases in exercising muscle. Magn Reson Med. 2002 Jan;47(1):14-23.
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. |
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