Ion movements and volume changes induced by catecholamines in erythrocytes of rainbow trout: effect of pH.

1. Trout red cells suspended in an isotonic medium containing catecholamines or adenosine 3',5'-phosphate (cyclic AMP) enlarge rapidly to reach a new steady-state volume which is maintained as long as hormone is present. 2. The present investigation demonstrates that the maximum swelling reached by the cells is strongly pH dependent. At pH 7.55 the cells enlarge more rapidly than at pH 7.95 and they reach a maximal volume which is much greater. It is explained by a differential effect of pH on two pathways controlling the movements of cations: K+ loss decreases as pH becomes more acidic in a roughly linear manner. On the contrary Na+ uptake increases as pH becomes more acidic with a maximum around pH 7.30 and then decreases. From this pH dependence it can be expected that the maximum enlargement occurs at about pH 7.30. 3. The complex relationship describing the change in the activity of the Na+-H+ exchanger as a function of pH (bell-shaped curve) is explained by the predominant influence of internal H+ on the antiporter in the alkaline range of pH and by the predominant influence of external H+ on the transporter in the acidic range.