Evidence for Na+/H+ antiport in cultured dog kidney cells (MDCK).

The relationship between sodium transport and the intra- and extracellular pH was examined employing dog kidney epithelial cells (MDCK). Increases in the medium pH led to a stimulation of 22Na+ influx and an inhibition of efflux. Kinetic analysis of the pH effects showed that the apparent Km values for Na+ were substantially altered (28 mM at pH 9 versus 95 mM at pH 6), indicating that H+ and Na+ ions competed for the extracellular binding sites of the transport system. Addition to the medium of organic acids, such as acetate and isobutyrate, led to an enhancement of the initial rate of 22Na+ uptake into sodium-depleted cells and to an induction of dome formation by monolayer cultures. [14C]Dimethyloxazolidinedione (DMO) was used to estimate the pH gradient across the cell membrane. [14C] DMO uptake in the presence of the respiratory chain inhibitor, antimycin, was influenced by the extracellular pH as well as by the addition of sodium to the medium. Sodium and lithium, but not potassium, were capable of increasing the cellular [14C]DMO concentration by an amiloride-sensitive mechanism. These increases were largely unaltered when valinomycin and 3.5 mM K+ were present in the uptake buffer, a condition designed to diminish any Na+-induced changes in the membrane potential. The results are consistent with the existence of a Na+-H+ antiport system in MDCK cells. The significance of this system is discussed.