Root effect induced by CO2 and by fixed acid in the blood of the eel, Anguilla anguilla

The decrease in O2 capacity with decreasing pH (Root effect) was studied in eel blood in which pH was varied in the range 5 to 9 both by addition of acid or base (fixed-acid Root effect) and by varying PCO2 (CO2 Root effect). Hemoglobin-bound oxygen was independent of PO2 above 150 Torr and was thus referred to as O2 capacity (O2cap). At pH below 8.5, O2cap decreased sigmoidally with pH to attain, below a pH of 6.0, a value which, at 15 degrees C, averaged about 48% of the maximum O2cap, measured above pH 8.5. At 25 degrees C, this reduction was even more pronounced. For pH above about 6.5 the decline in O2cap was independent of whether the pH was diminished by CO2 or by fixed acid. Below pH 6.5, however, the CO2 Root effect exceeded the fixed-acid Root effect. Below pH of 7.5, the buffer value of true plasma increased with declining pH and attained a negative value in the range where CO2 exerted a specific action on the Root effect.