Metabolism and transport of L-glutamine and L-alanine by renal tubules of chickens.

The metabolism and cellular transport of 1 and 5 mM glutamine (Gln) and alanine (Ala) and the metabolism of lactate (Lac) by renal tubular fragments of normal and chronically acidotic chickens were studied. The tubules were prepared by the collagenase digestion procedure and incubated for 0-60 min with or without substrates. Acidosis increased 1 mM Gln utilization from 1.14 to 1.74 and 1 mM Ala from 1.55 to 2.92 mumol X min-1 X g wet wt-1. Gluconeogenesis increased from 0.29 to 0.59 (Gln) and 0.44 to 1.06 (Ala), while ammoniagenesis rose from 2.19 to 3.24 (Gln) and 1.54 to 2.56 (Ala) mumol X min-1 X g-1. In contrast, Lac uptake (2.71 mumol X min-1 X g-1) and gluconeogenesis from Lac (1.05 mumol X min-1 X g-1), which equalled or exceeded the values observed with Gln or Ala in normal rats, were unchanged by acidosis. These data suggest 1) that acidosis increases gluconeogenesis from Gln and Ala by accelerating the glutamate deamination process, and 2) that the glutamate originating from glutamine and alanine are segregated in two different pools within the mitochondria with different access to glutamate dehydrogenase activity. Net cellular uptake of Gln was greater in acidotic chicken tubules, establishing an intracellular concentration of 4.5 in acidotic vs. 3.0 mM in normal chickens when 1 mM Gln was used in the incubation medium. In contrast, 1 mM alanine uptake was not modified by acidosis, greater intracellular metabolism lowering the cellular concentration of this amino acid. These observations suggest that the cellular transport of glutamine but not that of alanine is increased in tubular fragments of acidotic chickens.