Factors influencing the pH of sea lamprey (Petromyzon marinus) erythrocytes were examined in vitro. The absence of extracellular Na+ caused a significant reduction in the erythrocyte pH. In addition, the protonophore 2,4-dinitrophenol was capable of reducing the erythrocyte pH when it was dissolved in dimethyl sulfoxide. In the presence of ouabain, a step increase in the carbon dioxide tension caused a large increase in the intracellular Na+ concentration, but the rate of increase was considerably reduced after the 1st hour. Even in the absence of ouabain, however, the intracellular Na+ concentration in erythrocytes equilibrated with 3% CO2 is much greater than that in erythrocytes equilibrated with 0.2% CO2. Together, these results suggest that Na+-dependent H+ movements, possibly Na+–H+ exchange, may have an important role in erythrocyte pH regulation in P. marinus. Moreover, the mechanism appears to be stimulated by the decrease in extracellular or erythrocyte pH associated with the increase in [Formula: see text]. Extracellular Na+ also has a significant impact on the CO2-transport properties of P. marinus blood. In the absence of extracellular Na+, the intracellular total CO2 concentration was significantly reduced, whereas extracellular total CO2 concentration, [Formula: see text], was significantly increased. Furthermore, in the no-Na+ saline, [Formula: see text] became dependent on the hematocrit; an increase in the number of erythrocytes resulted in an increase in [Formula: see text]. This result suggests that the erythrocyte membrane of P. marinus may be permeable to [Formula: see text].
1529 FACTORS INFLUENCING TRANSCUTANEOUS CARBON DIOXIDE MEASUREMENT (tccO2) IN NEONATES