Acid-base regulation during exercise and recovery in the blue crab, Callinectes sapidus

During swimming activity Callinectes sapidus incurred a severe hemolymph acidosis due to elevated levels of PCO2 and lactate. Although hemolymph lactate concentration rose steadily during 1 h of exercise, hemolymph pH was maximally depressed within the first 15 min. A discrepancy between the quantities of lactate and H+ released from the tissues into the hemolymph is explained by a large apparent efflux of H+ into the ambient seawater, presumably via a branchial ion exchange process. Ammonia excretion increased 6 fold during exercise, but it is not clear if this contributed to the excretion of H+. The total quantity of H+ excreted into the environment during exercise and recovery far exceeded that which could be attributed to hemolymph lactic acid, indicating that some of the excreted H+ must have originated from other sources, such lactic acid which dissociated intracellularly, with the lactate anions remaining in the cells. Because lactate anions increase hemocyanin O2 affinity when unopposed by the Bohr shift, the excretion of a large portion of the metabolic H+ load, leaving lactate behind in the hemolymph, has important consequences for the regulation of O2 transport during swimming.