Sodium and Potassium Fluxes and Membrane Potential of Human Neutrophils

Sodium and potassium ion contents and fluxes of isolated resting human peripheral polymorphonuclear leukocytes were measured . In cells kept at 37 °C, [Na]i was 25 mM and [K]i was 120 mM; both ions were completely exchangeable with extracellular isotopes . One-way Na and K fluxes, measured with 22Na and 42K, were all -0.9 meq/liter cell water -min . Ouabain had no effect on Na influx or K efflux, but inhibited 95 t 7% of Na efflux and 63% of K influx . Cells kept at 0°C gained sodium in exchange for potassium ([Na]i nearly tripled in 3 h) ; upon rewarming, ouabain-sensitive K influx into such cells was strongly enhanced . External K stimulated Na efflux (Km ^-1 .5 mM in 140-mM Na medium) . The PNa/PKpermeability ratio, estimated from ouabaininsensitive fluxes, was 0.10 . Valinomycin (1 AM) approximately doubled PR . Membrane potential (V.) was estimated using the potentiometric indicator diSC3(5) ; calibration was based on the assumption of constant-field behavior . External K, but not Cl, affected Vm . Ouabain caused a depolarization whose magnitude depended on [Na]i . Sodium-depleted cells became hyperpolarized when exposed to the neutral exchange carrier monensin; this hyperpolarization was abolished by ouabain . We conclude that the sodium pump of human peripheral neutrophils is electrogenic, and that the size of the pump-induced hyperpolarization is consistent with the membrane conductance (3.7-4.0 /IS/ cm2) computed from the individual K and Na conductances .