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

Abstract

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 (K½10−4moll−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 pHo, 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 CI−/HCO3− exchange with an increased rate of Na+ pumping and next KCl 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.