Phosphorylation state of red and white muscle in tilapia during graded hypoxia: an in vivo P-31-NMR study

The aim of this study was to measure the energetic consequences of hypoxia in different types of skeletal muscle within a single tilapia species (n = 5). To that aim, 81.0 MHz P-31-nuclear magnetic resonance (NMR) spectra wer e collected, alternately, from three surface coils placed adjacent to the t issues of interest (dorsal white muscle, ventral white muscle, and lateral red muscle) during a graded hypoxia load over 6 h followed by a 5-h recover y period. The fish were contained in a flow cell, enabling us full control of the oxygen content of the bathing medium. The intracellular pH and the c oncentrations of ATP, phosphocreatine (PCr), and P-i were determined from t he NMR spectra. For normoxia, biochemical differences for [gamma-ATP], [PCr ], and [sugar phosphates] (SP) were observed between all three locations, e specially between the red and white muscle. During hypoxia stress, loss of phosphorylated compounds (PCr+P-i+SP) was observed at all locations but was the most severe in red muscle. When the aerobic (respirometry) and anaerob ic (P-31-NMR) ATP production via an energy balance are compared, flexible m etabolic depression is demonstrated during anaerobioses. It is concluded th at control of the aerobic and anaerobic component of metabolism during meta bolic depression is independent of each other.