Adrenalin-Induced Na+/H+ Exchange In Trout Erythrocytes and its Effects Upon Oxygen-Carrying Capacity

Addition of adrenalin (10−4moll−1) to trout erythrocytes in an unbuffered saline resulted in a rapid acidification of the extracellular medium. This process was inhibited by amiloride (K1/2∼10−4moll−1) and by the removal of extracellular Na +. The rate of acidification was a saturable function of extracellular Na+ concentration. When extracellular pH was maintained constant by continual titration with KOH, adrenalin induced a transient burst of H+ efflux. During this period the loss of cellular H+ equivalents was approximately equal to the net gain of Na+, providing evidence for a Na+/H+ exchange with a stoichiometry of 1. The steady state following stimulation with adrenalin could be disturbed by changes in extracellular pH. After the addition of adrenalin, intracellular pH (pHi) was increased by 0·2–0·3 units but did not exceed extracellular pH, as required if the Na+ and H+ concentration ratios came into equilibrium. The increase in pHi in stimulated compared with control cells was maintained approximately constant over a wide range of pH0, suggesting that pH equilibration by the Jacob-Stewart cycle was operating normally and that the activation of Na+ / H+ exchange provides an offset to the normal relationship between pHi and pHo. The steady state results from a balance of an increase Na+/H+ and CD/HCO3− exchange with an increased rate of Na+ pumping and next KC1 efflux. In a buffered saline, adrenalin caused a 22–46 % increase in the oxygen-carrying capacity of trout erythrocytes. It is suggested that this was due to a Root effect of trout haemoglobin caused by cellular alkalinization when the Na+/H+ exchange mechanism was activiated. This observation suggests that many published values for oxygencarrying capacity of fish blood require re-evaluation.