Kinetic parameters for Na+-dependent HMA−sJH+ in MDCK cells.

Saturable extrusion rate of H+ (HMA−sJH+) was determined in MDCK cells cultured for 48 hours in culture medium without (–ATO) or with (+ATO) 0.05 µmol/L arsenic trioxide (ATO) dissolved in water in the presence of different extracellular concentrations of sodium (see Methods). Transport data represents the fraction inhibited by 5-N,N-hexamethylene amiloride (HMA, 5 µmol/L). KD is non-saturable HMA−sJH+ in the range of extracellular sodium used in the experiments, Vmax is the maximal velocity of HMA−sJH+, Km is the apparent Michaelis-Menten parameter of HMA−sJH+, Vmax/Km is the maximal transport capacity, 1/C/AsF is the relative effect of ATO on HMA−sJH+ compared with HMA−sJH+ in the absence of ATO. *P