SUMMARY
Mechanisms of intracellular pH (pHi) regulation were investigated in anoxia-tolerant hepatocytes from goldfish Carassius auratus, and compared to the situation in the anoxia-intolerant hepatocytes from trout Oncorhynchus mykiss. Under normoxic conditions, the pHi of goldfish hepatocytes was regulated by a Na+/H+ exchanger and a Na+-independent Cl–/HCO3– exchanger, the latter being activated only after acidification of the cells. Mechanisms of acid secretion appear to be fuelled, at least in part, by lactate formation under fully aerobic conditions, as inhibition of glycolysis caused a drastic reduction of steady state proton release. In trout hepatocytes both a Na+/H+ exchanger and a Cl–/HCO3– exchanger were found to be tonically active, as described previously. During chemical anoxia a constant pHi was maintained in goldfish hepatocytes, whereas it was reversibly reduced by 0.3 units in the trout cells. Under these conditions a reversible increase in the rate of acid secretion was induced in the cells from both species. In the goldfish cells this was based on a SITS-sensitive transporter, possibly involving export of lactate, with no contribution from Na+/H+ exchange. By contrast, in hepatocytes from trout, CN-induced acid secretion was dominated by the activity of the Na+/H+ exchanger. Brief exposure to extracellular acidosis had no dramatic effects on the energetics of hepatocytes from either species.