Stock solutions of bumetanide (10 mM) were prepared in 100 mM Tris base and used at a final concentration of 10 μM. Stock solutions of ouabain (10 mM) were prepared in distilled water and used at a final concentration of 100 μM. Stocks of clotrimazole (CLT; 5 mM) were prepared in DMSO and used at final concentrations of 5 μM. After washing whole blood and removal of plasma and buffy coat, in most experiments RBC suspensions were placed in tonometers (Eschweiler, Kiel, Germany) at 20% haematocrit (Hct), to equilibrate at the requisite O2 tension. Tonometers were flushed with warm, humidified gas mixtures, supplied at the appropriate O2 tension using a Wösthoff gas mixing pump. For CLT, dissolved in DMSO, appropriate controls were all treated with the same concentration of solvent (b0.1% final).