Contribution of net ion transfer mechanisms to acid-base regulation after exhausting activity in the larger spotted dogfish (Scyliorhinus stellaris).

Specimens of the larger spotted dogfish (Scyliorhinus stellaris) were electrically stimulated to exhaustion in a closed seawater recirculation system. The production of large quantities of lactic acid by anaerobic metabolism and the resultant efflux of the dissociation products, H+ and lactate, from the white musculature resulted in severe acid-base disturbances and in increases in plasma lactate concentration, the two effects having extremely different time courses. Plasma pH and bicarbonate were maximally depressed 15-30 min after exercise, whereas peak lactate concentrations of up to 30 mM were not attained before 4-8 h after exercise. The acid-base status were restored to normal 10-14 h after exercise, long before the aerobic processing of surplus lactic acid was complete 22-30 h after exercise. This behaviour can be explained on the basis of an interaction of transfer rates, buffer values and equilibria between intracellular and extracellular compartments with the transient net transfer of surplus H+ ions to the environmental water. About half of the original quantity of H+ was transferred net to the environment via the branchial epithelium during the first 8-10 h, and it was later taken up again at the rate of aerobic lactic acid processing in the metabolism of the fish, whereas a transfer of lactate was not observed at any time during the experiment. As a result, the distribution patterns of H+ and lactate differed from each other and varied with time elapsed after anaerobic exercise, leading to the apparent 'H+ ion deficit' which has been observed in the blood of several fish species during lactacidosis. Net transfer of H+ ions to the environment facilitates rapid normalization of the acid-base status long before the original stress, lactic acid, is removed from the organism and thus represents an effective regulatory mechanism for the defence of the internal milieu in fish.