Anaerobic Metabolism and Changes in Acid-Base Status: Quantitative Interrelationships and pH Regulation in the Marine Worm Sipunculus Nudus

Abstract

ABSTRACT The quantitative influence of anaerobic metabolism on acid-base status and on acid-base regulation is investigated in Sipunculus nudus L. Proton generation by metabolism is calculated from theoretical predictions. The quantitative comparison of metabolic protons with non-respiratory protons found in the acid-base status is performed assuming a simplified model of the total animal. Taking the protonequivalent ion exchange between animals and ambient water into account, changes in the anaerobic acid-base status can be explained exclusively by proton generation in metabolism. It is concluded that the classical concept of acid-base physiology is adequate and that the consideration of strong ions is not required for a quantitative treatment of the acid-base status. The hypothesis that a quantitative correlation exists between metabolic and acid-base events is tested by comparing changes in acid-base status and in metabolism in animals exhibiting different metabolic rates. For this purpose, a method is developed for the calculation of intracellular pH from metabolite concentrations and extracellular acid–base parameters. Proton exchange between intra-and extracellular compartments, which is found to depend upon the total amount of accumulated non-respiratory protons, demonstrates that pHi is regulated even during anaerobiosis. The defended pH1 value, however, is lower during anaerobiosis than during subsequent recovery.