Resistance to freshwater exposure in White Sea Littorina spp. II: Acid-base regulation

Parameters of acid-base and energy status were studied by in vivo P-31-nucl ear magnetic resonance spectroscopy in three White Sea Littorina spp. (L. l ittorea, L. saxatilis and L, obtusata) during prolonged anaerobiosis in fre shwater. Intracellular DF-I decreased significantly, especially during the early period of anaerobiosis, but later the decrease in intracellular pH sl owed down considerably, suggesting a capacity for intracellular pH regulati on in all three species. There was a trend for intracellular pH to fall mos t rapidly in the least freshwater-resistant species, L. ohtusata, as compar ed to the most resistant, L. littorea. Non-bicarbonate, non-phosphate buffe r values estimated by the homogenate technique were similar ill the three s tudied species (28-37 mmol pH(-1) kg(-1) wet weight) and did not change dur ing freshwater exposure. The CaCO3 buffer value of the foot tissues was con siderably higher (171-218 mmol pH(-1) kg(-1) wet weight) and decreased sign ificantly during freshwater exposure. The contribution of the multiple tiss ue buffering systems to intracellular pH regulation in Littorina spp. shift s between different stages of freshwater exposure. Initially. the non-bicar bonate, non-phosphate tissue buffering system seems to be of major importan ce for metabolic proton buffering at intracellular pH between 7.5 and 7.0. During later stages of anaerobiosis and at lower intracellular pH, the CaCO 3 buffer is involved in proton buffering. Decrease in the CaCO3 buffer valu e during freshwater exposure was in quantitative agreement with the amount of metabolic protons buffered, thus suggesting that CaCO3 tissue stores may serve as a major buffering system during prolonged anaerobiosis in Littori na spp.