Relationship between ATP level and respiratory rate in sea urchin embryos

In sea urchin embryos, the rate of respiration, as a result of electron transport through the mitochondrial respiratory chain, was enhanced after hatching without any change in the intrinsic capacity of electron transport in mitochondria. The increase in respiratory rate after hatching was accompanied by an evident decrease in intracellular adenosine triphosphate (ATP) concentration without any change in intracellular levels of adenosine diphosphate (ADP) and adenosine monophosphate (AMP). Adenosine triphosphate is proposed to fortify acceptor control of respiration at high concentrations and to reduce the respiratory rate even in the presence of ADP, the acceptor. The relationships between the respiratory rate and intracellular ATP concentration in embryos were the same as those in mitochondria isolated from embryos, obtained in the presence of ADP at the same concentration as in the embryos. Probably, the respiratory rate is enhanced after hatching because of the decrease in the level of ATP. In embryos kept in a medium containing adenosine, intracellular ATP concentration increased especially after hatching, without any change in the ADP level, and the respiratory rate after hatching was made as low as the rate expected, based on the relationships obtained on isolated mitochondria. The respiratory rate in embryos probably depends on intracellular ATP concentration, irrespective of the developmental stage in early development.