Quantitative modelling of the effects of selected intracellular metabolites on pH in fish white muscle

A model is presented that provides guidelines to the identification of key experimental variables influencing proton balance and intracellular pH in vertebrate white muscle. We have drawn on data from the literature on rainbow trout (Oncorhynchus mykiss) in an attempt to quantify the influence of metabolic, ionic and transport components of proton generation and proton consumption after exercise. Only minor changes in proton balance and in calculated intracellular pH were caused by considering changes in the concentration of bicarbonate or including the acid-base characteristics of purine nucleotides. Intracellular pH, as estimated by the model, was more acidic at some time points in recovery compared with in vivo measurements, and this would appear to result mainly from inaccuracies in quantifying the phosphate component of proton buffering. Nevertheless, the model was able to simulate the typical pattern of muscle acidosis and recovery observed for trout, including the transient post-exercise acidification and the slow recovery rate. As with previous pHi models, comparison of model estimates with experimental observations is essential in this approach in order to identify whether all of the relevant metabolic processes have been considered for accurate quantification of proton balance within the white muscle compartment.