Abstract
The effect of epinephrine in regulating erythrocytic nucleotide triphosphate (NTP) concentrations was examined in blood and erythrocytes from Fundulus heteroclitus. Epinephrine decreased the NTP/hemoglobin (NTP/Hb) ratio by 44% over the Pco₂ range of 1.5-7.6 mmHg. Decreases in erythrocytic pH, caused by increases in Pco₂, mediated the extent to which reduced NTP concentrations increased Hb O₂ afinity. Both the Na⁺/K⁺ pump and Cl⁻/HCO⁻₃ exchange were involved in lowering erythrocyte NTP concentrations. Epinephrine stimulation, alone or in the presence of amiloride or ouabain, had no effect on erythrocyte pH. A marked intracellular alkalinization occurred in the presence of SITS (4acetamide-4-isothyocyanato-stilbene). The data suggest that the Cl⁻/HCO⁻₃ and Na⁺/H⁺ exchange are tightly coupled and responsible for maintenance of transmembrane pH. Finally, the decrease in erythrocyte NTP concentration following epinephrine stimulation was not accompanied by an increase in intracellular pH, which indicates that Donnan equilibrium was not maintained. This suggests that the Cl⁻/HCO⁻₃ exchange may be active in F. heteroclitus erythrocytes.
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