Oxygen uptake on-kinetics in dog gastrocnemius in situ following activation of pyruvate dehydrogenase by dichloroacetate

Abstract

The aim of the present study was to determine whether the activation of the pyruvate dehydrogenase complex (PDC) by dichloroacetate (DCA) is associated with faster O(2) uptake (V(O2)) on-kinetics. V(O2) on-kinetics was determined in isolated canine gastrocnemius muscles in situ (n = 6) during the transition from rest to 4 min of electrically stimulated isometric tetanic contractions, corresponding to approximately 60-70 % of peak V(O2). Two conditions were compared: (1) control (saline infusion, C); and (2) DCA infusion (300 mg (kg body mass)(-1), 45 min before contraction). Muscle blood flow (Q) was measured continuously in the popliteal vein; arterial and popliteal vein O(2) contents were measured at rest and at 5-7 s intervals during the transition. Muscle V(O2) was calculated as Q multiplied by the arteriovenous O(2) content difference. Muscle biopsies were taken before and at the end of contraction for determination of muscle metabolite concentrations. DCA activated PDC at rest, as shown by the 9-fold higher acetylcarnitine concentration in DCA (vs. C; P < 0.0001). Phosphocreatine degradation and muscle lactate accumulation were not significantly different between C and DCA. DCA was associated with significantly less muscle fatigue. Resting and steady-state V(O2) values during contraction were not significantly different between C and DCA. The time to reach 63 % of the V(O2) difference between the resting baseline and the steady-state V(O2) values during contraction was 22.3 +/- 0.5 s in C and 24.5 +/- 1.4 s in DCA (n.s.). In this experimental model, activation of PDC by DCA resulted in a stockpiling of acetyl groups at rest and less muscle fatigue, but it did not affect 'anaerobic' energy provision and V(O2) on-kinetics.

Figure 1. Fatigue index

Mean (± s.e.m.) values of fatigue index (average values of force determined every 10 s/initial force) as a function of time of contraction in the two experimental conditions, control (C) and dichloroacetate (DCA) administration. * Statistically significant difference.

Figure 2. Mean (± s.e.m.) values of muscle blood flow, arterio-venous O₂ concentration difference and muscle O₂ uptake

The vertical dashed lines indicate the onset of contraction.

Figure 3. Individual values of muscle O₂ uptake

Points at time 0 indicate the resting baselines. The best-fitting curves (see Methods) are also shown.

Figure 4. Parameters of muscle O₂ uptake on-kinetics

Mean (± s.e.m.) values of calculated times (see Methods) to reach 50 % (t_50%) and 63 % (t_63%) of differences between resting baselines and steady-state values obtained towards the end of contraction, for the V̇_O2 on-kinetics in the two experimental conditions.