Effect of systemic pH on pHi and lactic acid generation in exhaustive forearm exercise.
To investigate whether changes in systemic pH affect intracellular pH (pHi), energy-rich phosphates, and lactic acid generation in muscle, eight normal volunteers performed exhaustive forearm exercise with arterial blood flow occluded for 2 min on three occasions. Subjects ingested 4 mmol/kg NH4Cl (acidosis; A) or NaHCO3 (alkalosis; B) or nothing (control; C) 3 h before the exercise. Muscle pHi and phosphocreatine (PCr) content were measured with 31P-nuclear magnetic resonance (31P-NMR) spectroscopy during exercise and recovery. Lactate output during 0.5-7 min of recovery was calculated as deep venous-arterial concentration differences times forearm blood flow. Before exercise, blood pH and bicarbonate were lower in acidosis (7.303 +/- 0.009, 18.6 +/- 0.5 meq/l) than alkalosis (7.457 +/- 0.010, 32.2 +/- 0.7 meq/l) and intermediate in control (7.389 +/- 0.007, 25.3 +/- 0.6 meq/l). Lactic acid output during recovery was less with A (245 +/- 39 mumol/100 ml) than B (340 +/- 55 mumol/100 ml) (P less than 0.05) and intermediate in C (293 +/- 31 mumol/100 ml). PCr utilization and resynthesis were not affected by extracellular pH changes. pHi did not differ before exercise (A, 7.04 +/- 0.01; B, 7.09 +/- 0.01; C, 7.06 +/- 0.01) or at its end (A, 6.28 +/- 0.07; B, 6.28 +/- 0.11; C, 6.31 +/- 0.09). Hence systemic acidosis inhibited and alkalosis stimulated lactic acid output. These findings suggest that systemic pH regulates cellular acid production, protecting muscle pH, at the expense of energy availability.
Hood
V L
VL
Kantonsspital, University of Basel, Switzerland.
Schubert
C
C
Keller
U
U
Müller
S
S
D000328:Adult; D001639:Bicarbonates / Q000097:blood; D005542:Forearm / Q000098:blood supply / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D009132:Muscles / Q000098:blood supply / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism; D005082:Physical Exertion; D010991:Plethysmography; D012039:Regional Blood Flow
D001639:Bicarbonates; D007773:Lactates; D010725:Phosphocreatine