Glutamine Transport in Rat Kidney Mitochondria in Metabolic Acidosis

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Abstract
In order to study factors regulating renal ammoniagenesis, the transport and metabolism of L-glutamine were studied in mitochondria from kidneys of control and acidotic rats. On incubation in 1 mM [14C]glutamine, there was production and accumulation of [14C]glutamate within the matrix space. However no [14C]glutamine was detected in the matrix space, even with 10 mM [14C]glutamine as substrate or with inhibition of glutamine deamidation (low temperature, p-chloromercuribenzoate, mersalyl). These results suggest that glutamine crosses the inner membrane by a carrier-mediated step and that this step is rate-limiting in glutamine deamidation. In chronic acidosis there is a fourfold increase in the uptake of radioactivity from [14C]glutamine, but not from α-ketoglutarate, glutamate, or acetate. In 3-h acidosis, before any increase in extracted glutaminase levels, there is a significant and reproducible increase (39±3.8%, n = 25) in matrix uptake of radioactivity from [14C]glutamine and also an increased ammonia production (17±3.7%, n = 12). Administration of furosemide produces a similar degree of potassium depletion and a greater degree of sodium depletion over 3 h when compared to a 3-h acidosis. However, it produces no change in mitochondrial uptake of radioactivity. These results show that the adaptation of renal glutamine metabolism observed in acidosis is due to the acidosis and is demonstrable in isolated rat kidney mitochondria. The site of adaptation is in the carrier system, which transports glutamine across the inner membrane. The increased transport in acidosis delivers more glutamine to glutaminase, which results in the increased renal ammonia production.