A kinetic analysis of Na-Li countertransport in human red blood cells.
We examined the kinetic properties of the interactions between inner and outer cation sites of the Na-Li countertransport system in human red blood cells. Li-stimulated Na efflux [V(Na)] was measured as a function of external Li [(Li)o] and internal Na [(Na)i] contents. At each (Li)o, a Hanes plot of (Na)i/V(Na) vs. (Na)i allowed us to calculate the apparent dissociation constant for internal Na (KiNa) and the maximal rate of Na efflux [Vmax(Na)]. In erythrocytes from 10 different subjects, the Vmax(Na)/KiNa ratios were independent of the external Li concentrations. In other experiments, Na-stimulated Li efflux [V(Li)] was measured as a function of external Na and internal Li contents. In three subjects studied, the Vmax(Li)/KiLi ratios were independent of the external Na concentrations. The data strongly suggest that the countertransport mechanism is consecutive ("ping-pong").
Hannaert
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PA
Garay
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D000328:Adult; D001693:Biological Transport, Active; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D007700:Kinetics; D008094:Lithium / Q000097:blood*; D008297:Male; D008954:Models, Biological; D012964:Sodium / Q000097:blood*
D007473:Ion Channels; D008094:Lithium; D012964:Sodium