Renal mitochondrial glutamine metabolism and dietary potassium and protein content. Glutamine distribution, glutamate accumulation, phosphate-dependent glutaminase (PDG) concentrations and intact mitochondrial ammonia production were studied in renal mitochondria from rats fed low, normal and high potassium diets and in mitochondria from rats fed high or low protein diets. The rats given a low potassium diet were potassium-depleted by 10 to 20% but in none of the groups were there any abnormalities of extracellular acid-base status. Glutamine was present in the outer space of mitochondria but could not be depleted in the matrix space in any group. In both the potassium-depleted and the high protein animals, we found increased matrix -14-C-uptake of glutamine (as -14-C-glutamate), increased intact mitochondrial ammonia production and increased concentrations of PDG. In the K+-depleted group there was a decreased matrix -14C-uptake when -14C-gamma-ketoglutarate of -14C-glutamate was present in the medium. Potassium loading produced no change in mitochondrial glutamine metabolism. Protein loading (compared with protein depletion) and potassium depletion induce an increased uptake of glutamine into the renal mitochondrial matrix space which leads to its increased deamidation. This adaption may explain the increased renal ammonia production seen in these situations when compared to their respective controls.