Organization of energy provision in rainbow trout during exercise.

The purpose of this investigation was to examine the fuels supporting high-intensity progressive exercise and their regulation within rainbow trout. During the sustained swim, red muscle (RM) used 97% (17.5 mumol/g) of its glycogen, whereas white muscle (WM) glycogen only declined 31% (7.3 mumol/g). During the burst swim, WM glycogen content decreased 10.4 mumol/g at a rate that exceeded the sustained swim rate by 6.2-fold. Lactate content increased 11-fold at a rate 25 times its sustained swim rate. The exhaustive swim resulted in a decrease of 36.6 mumol/g in liver glycogen, whereas WM glycogen content declined to very low values and lactate reached 43 mumol/g. RM glycogen levels remained low during these exercise bouts. Phosphocreatine (PCr)-buffered ATP declines (WM 7.3-2.7 mumol/g, RM 3.4-1.6 mumol/g) with the time course of the large ATP decreases being related to near depletion of PCr. Decreases in the total adenylate pool were compensated for by the accumulation of inosine 5'-monophosphate in both tissue types. Free ADP (ADPf) contents increased in both tissues by three- to fivefold. ATP/ADPf and cytosolic phosphorylation potentials decreased from 7- to 20-fold. Cytosolic redox potential remained relatively constant at approximately 145 within both fiber types. The changes in adenine nucleotide parameters are associated with the respective activation of the different fiber types and glycolytic flux.