Impaired cation transport in thymocytes of rats with chronic uremia includes the Na+/H+ antiporter

To examine how uremia changes sodium, potassium, and proton transport, thymocytes from chronic renal failure (CRF) rats were studied. If alterations in cation transport associated with chronic uremia (CRF) extend to intracellular pH regulation, the susceptibility to the catabolic effects of acidosis might be increased. To evaluate the influence of acidosis, cation transport in thymocytes from normal rats with NH4Cl-induced acidosis was also studied. Ouabain-sensitive 86Rb influx in thymocytes from acidotic CRF rats was 32% lower than in control cells (P < 0.05), but intracellular sodium concentration was unchanged. This may be related to a 47 +/- 22% reduction in 22Na influx. In thymocytes from nonuremic, acidotic rats, ouabain-sensitive 86Rb influx was decreased 39% (P < 0.025), similar to the change in CRF. In CRF thymocytes, Na(+)-H+ antiporter activity in response to cell acidification (7.13 +/- 0.8 versus 9.42 +/- 0.8 mmol of H+/L per min; CRF versus control), or to osmotic shrinkage (0.43 +/- 0.09 versus 0.82 +/- 0.11 mmol of H+/L per min; CRF versus control), was significantly (P < 0.01) reduced. Buffering capacity at resting and acidic intracellular pH was unchanged by uremia, but Na+/H+ antiporter activity in response to acid loading or osmotic shrinkage was unchanged in thymocytes of nonuremic rats with metabolic acidosis. Thus, CRF reduces both Na/K-ATPase and Na+/H+ antiporter activities in rat thymocytes. The former may be secondary to reduced sodium influx. Impaired Na+/H+ antiporter activity is not caused by metabolic acidosis alone, whereas reduced Na/K-ATPase activity is found in both acidosis and uremia.