['Potassium transport via the potassium chloride cotransporter in rainbow trout erythrocytes is increased by high oxygen tension. It appears that the effect of oxygen is mediated by reactive oxygen species, especially hydroxyl radicals. In contrast, the activity of adrenergically stimulated sodium proton exchange decreases with increasing oxygen tension. As available data suggest that the two transporters are regulated reciprocally, the present study was undertaken to evaluate, if hydroxyl radicals may inhibit sodium transport via the adrenergically stimulated sodium proton exchanger.', 'The effects of the hydroxyl radical scavenger, 2 mm mercaptopropionyl glycine (MPG), on the activity of the adrenergically activated sodium proton exchange in rainbow trout erythrocytes were examined by measuring unidirectional sodium flux, using radioactive isotope, and cellular water content.', 'The activity of the sodium proton exchange increased with decreasing oxygen tension after adrenergic stimulation. When MPG was present during incubation, there was no statistically significant effect of oxygen tension on the adrenergically stimulated sodium proton exchange, whereby the activity of the transporter at atmospheric oxygen tension was markedly higher in the presence than in the absence of MPG. In the absence of adrenergic stimulation, MPG did not influence the transporter activity significantly at any oxygen tension.'] Is oxygen dependency of the adrenergic Na/H exchange in rainbow trout erythrocytes diminished by a hydroxyl radical scavenger?