Effect of alloxan on phosphate transport in isolated mouse liver mitochondria: influence of pH, and differentiation between influx and efflux of phosphate

The effect of alloxan on inorganic phosphate (Pi) transport in isolated mouse liver mitochondria was studied by swelling techniques. Mitochondria preincubated with alloxan exhibited inhibition of Pi uptake assessed by NH4-Pi, K+-ionophore and acetate/Pi exchange systems, and also inhibition of Pi efflux assessed by the K+-ionophore and FCCP1-ATP systems. The effect on Pi uptake was pH dependent. Swelling in the FCCP-ATP system in the presence of alloxan and NEM was unaffected by rotenone and cysteine but was blocked by oligomycin, whereas the swelling caused by mersalyl was unaffected by rotenone, blocked by oligomycin, and reversed by cysteine. Alloxan stimulated mitochondrial ATPase activity, this effect being blocked by oligomycin. These findings suggest that alloxan causes an irreversible and pH-dependent inhibition of Pi influx and efflux in isolated mouse liver mitochondria.