Effects of in vitro potassium on ammoniagenesis in rat and canine kidney tissue

Effects of in vitro potassium on ammoniagenesis in rat and canine kidney tissue. Decreased ammonium (NH4+) excretion is associated with hyperkalemia. To determine if potassium could directly influence renal ammonia production, we investigated ammoniagenesis by rat and canine renal cortical tissues in vitro at different potassium concentrations. Renal tissue from normal and acidotic rats and normal dogs incubated in glutamine, lactate, and 7 to 10mEq/liters of potassium or 25mEq/liters of potassium produced significantly less ammonia than slices incubating in glutamine, lactate, and 4 to 5mEq of potassium. Glutamate accumulation, which follows glutamine deamidation, did not decrease and even increased at 25mEq/liters of potassium. With glutamine as the sole substrate, decreased ammoniagenesis was seen only at higher potassium concentrations (> 16mEq/liters) than when lactate was also present. The depression to glutamine ammoniagenesis by high concentrations of potassium was partially obliterated in an anaerobic environment. When glutamate replaced glutamine as the precursor, renal ammonia produced by slices in 7 and 25mEq/liters was again significantly lower than by slices incubating in 4mEq/liters. We blocked glutamine synthesis by rat kidney slices with dl-methionine dl-sulfoximine when glutamate was the renal ammonia precursor. This essentially allows glutamate deamination to produce ammonia. Potassium depressed glutamate deamination significantly at 7mEq/liters (↓ 13%) and at 25mEq/liters of potassium (↓ 35%) as compared to 4mEq/liters. The above findings are consistent with a major depressive effect of in vitro potassium on glutamate deamination in rat and canine kidneys. Other evidence, especially from rat tissue studies, suggests that potassium also may affect glutamine deamination directly. Rat kidney slices incubating in the high potassium medium of 7mEq/liter or greater also consumed less oxygen in the presence of glutamine (P < 0.01), oxidatively decarboxylated less glutamine (P < 0.02) and produced less glucose from glutamine (P < 0.01). Effet du potassium in vitro sur l'ammoniogenèse dans tissu rénal de rat et de chien. Une diminution de l'excrétion d'ammoniaque (NH4+) est associée à l'hyperkaliémie. Afin de déterminer si le potassium peut influencer directement la production rénale d'ammoniac, nous avons étudié l'ammoniogenèse dans le tissu rénal cortical de rat et de chien in vitro à différentes concentrations de potassium. Du tissu rénal pro