The rate of sodium-lithium countertransport in red cells is thought to be determined by inheritance and to be constant over years in a given person. We have found that the rate is influenced acutely by ultrafiltration and by hemodialysis. In seven patients with endstage renal disease secondary to essential hypertension, the mean rate of sodium-lithium countertransport (+/- S.E.M.) was reduced from 0.18 +/- 0.02 to 0.09 +/- 0.01 mmol per liter of cells per hour (P less than 0.02) by ultrafiltration and from 0.22 +/- 0.03 to 0.12 +/- 0.03 mmol per liter per hour (P less than 0.001) by hemodialysis. When patients' red cells obtained before dialysis were incubated with plasma obtained afterward, the rate of countertransport fell, and when red cells obtained after dialysis were incubated with plasma obtained beforehand, the rate returned to normal. Whereas the rate in red cells from normal subjects was reduced after incubation in post-dialysis plasma from patients, predialysis plasma from the same patients had no such effect. We conclude that the rate of the countertransport system of red cells is dependent on a dialyzable plasma factor.
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