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Journal of Experimental Biology 118,229-246 (1985)
Published by Company of Biologists 1985

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

A. R. COSSINS ¹ and P. A. RICHARDSON ¹

¹ Department of Zoology, University of Liverpool, Liverpool L69 3BX, U.K.1

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 (K10^-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 (pH_i) 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 pH_i in stimulated compared with control cells was maintained approximately constant over a wide range of pH_o, 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 pH_i and pH_o. 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.

Key words: Trout erythrocytes, Na⁺/H⁺ exchange, amiloride, HCO₃^-/Cl^- exchange, adrenalin

Accepted on March 1, 1985

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