Predicting in vivo oxygen consumption rate from ETS activity and bisubstrate enzyme kinetics in cultured marine zooplankton

Abstract

Oxygen consumption rates ($R_{{{\text{O}}_{2} }}$) in the rotifer Brachionus plicatilis and the mysid Leptomysis lingvura during both well-fed conditions and starvation have been modeled using the electron transport system (ETS) activity, bisubstrate kinetics and intracellular concentration of substrates. Furthermore, the influence of the food quality on the respiratory metabolism and metabolite levels has been explored. The highest values of most of the variables both in rotifers and mysids were mainly found on organisms grown on the lipid-rich diet, although no differences were determined between treatments in the response to starvation. Time courses of the $R_{{{\text{O}}_{2} }}$ and the concentration of pyridine and adenine nucleotides evidenced a sharp decrease during food shortage and a fast recovery with food restoration, whereas the potential respiration (Φ) remained fairly constant. In general, the modeled $R_{{{\text{O}}_{2} }}$ ($V_{{{\text{O}}_{2} }}$) predicted with a high degree of success in the in vivo $R_{{{\text{O}}_{2} }}$, even though it yielded relatively lower values. Nonetheless, the correlation of the measured $R_{{{\text{O}}_{2} }}$ with $V_{{{\text{O}}_{2} }}$ during starvation was much better than with the $R_{{{\text{O}}_{2} }}$ estimated from ETS measurements and a fixed $R_{{{\text{O}}_{2} }}$/Φ ratio. Finally, the observed relationship between the measured $R_{{{\text{O}}_{2} }}$ and the adenine nucleotide ADP suggests that the contribution of this nucleotide should be included in future applications of this model.