Author(s): ROBERGS, R., NALOS, M., KELBICH, P., JIZEROVA, A., MERVARTOVA, I., VOSTRY, M., STENGL, M., BABUSKA, V., Institution: JAN EVANGELISTA PURKYNĚ UNIVERSITY IN ÚSTÍ NAD LABEM FACULTY OF SCIENCE: UNIVERZ, Country: CZECH REPUBLIC, Abstract-ID: 139

INTRODUCTION:
For more than 100 years it has been assumed that during intense exercise, skeletal muscle and blood become acidic from the excess production of metabolic acids, such as lactic acid. Considerable research opposes this assumption. The purpose of this research was to quantify the involvement of hydrogen ions (H+) in pertinent chemical reactions of skeletal muscle cytosolic energy catabolism through measurement of their pH to time profiles.
METHODS:
Aqueous reagents were prepared for chemical reactions using deionized water, substrates at known concentrations, and needed activator chemicals and enzymes. The chemical reactions studied, based on enzyme name, were the ATPase, creatine kinase (CKase), hexokinase (HKase), phosphofructokinase (PFKase), glyceraldehyde-3-phosphate dehydrogenase (G3PDHase), pyruvate kinase (PKase), D- and L- lactate dehydrogenase (LDHase) and glucose-6-phosphate dehydrogenase (G6PDHase). Where appropriate, both directions of the chemical reactions were studied. The reagent pH was adjusted with known quantities of base or acid to targeted start pH values. Each chemical reaction was started by the addition of the pertinent enzyme. The pH of the reagent was measured intermittently using a pH electrode at 25 C, and data was acquired at different intervals depending on conditions of individual, combined, or sequenced reactions. Samples of reagent (200 uL) were acquired intermittently for product measurement using spectrophotometry.
RESULTS:
The pH responses, structured by pH=start, adjusted, end reaction, and peak product ([P]) = x mmol.L-1 (for a subset of the reactions) were as follows: ATPase to ADP (pH=3.92, 8.4, 6.92), CKase to ATP (pH=4.8, 6.4, 7.2), CKase to creatine phosphate (CrP) (pH=4.02, 8.13, 7.5, [P]=0.64), HKase to glucose-6-phosphate (G6P) (pH=4.0, 8.65, 6.55, [P]=0.9), PFKase to fructose 1,6, bisphosphate (F1,6P) (pH=5.94, 8.37, 6.87), G3PDHase (2.97, 8.0, 7.81), LDHase to lactate (pH=6.9, 6.5, 10.0, [P]=0.6), LDHase to pyruvate (pH=5.6, 9.0, 7.2, [P]=0.35), G6PDHase to G6P (pH=3.25, 8.11, 6.75, [P]=0.9). The pH responses were similar for D- and L-LDH. Sequenced and combined chemical reactions revealed evidence of the summation of H+ exchange and accompanied pH responses.
CONCLUSION:
Chemical reactions that involve a H+ as a substrate or a product directly alter the pH of the aqueous solution consistent to the organic chemistry of the reaction. The chemical reactions of cytosolic energy catabolism do not produce molecules as acids. The implications of these results to the skeletal muscle and systemic acidosis during intense exercise performance need to be further researched, as is also true for the implications of the causes of metabolic acidosis in individuals with severe infection or disease, and the associated ‘best’ treatment options. The roles of lactate to exercise performance, and the methods and interpretations of lactate-based performance assessment need continued re-evaluation and changed where appropriate.