Effects of pH on beta-hydroxybutyrate transport in rat erythrocytes and thymocytes.
Entry of beta-hydroxybutyrate into erythrocytes and thymocytes is facilitated by a carrier (C), as judged from temperature dependence, saturation kinetics, stereospecificity, competition with lactate and pyruvate, and inhibition by moderate concentrations of methylisobutylxanthine, phloretin, or alpha-cyanocinnamate. We studied the dependence of influx and efflux on internal and external pH and [beta-hydroxybutyrate]. Lowering external pH from 8.0 to 7.3 to 6.6 enhanced influx into erythrocytes by lowering entry Km from 29 to 16 to 10 mM, entry V being independent of external pH. Lowering external pH inhibited efflux. At low external pH, external beta-hydroxybutyrate enhanced efflux slightly. At high external pH, external beta-hydroxybutyrate inhibited efflux. Internal acidification inhibited influx and internal alkalization enhanced influx. Internal beta-hydroxybutyrate (betaHB) enhanced influx more in acidified than alkalized cells. These data are compatible with coupled betaHB-/OH- exchange, betaHB- and OH- competing for influx, C:OH- moving faster than C: betaHB-, empty C being immobile. They are also compatible with coupled betaHB-/H+ copermeation, empty C moving inward faster than H+:C:betaHB-, H+:C being immobile, and C:betaHB- (without H+) being so unstable as not to be formed in significant amounts (relative to C, H+:C, and H+:C:betaHB-).
D000818:Animals; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability; D004912:Erythrocytes / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006885:Hydroxybutyrates / Q000097:blood*; D008564:Membrane Potentials; D008954:Models, Biological; D009994:Osmolar Concentration; D051381:Rats; D013601:T-Lymphocytes / Q000378:metabolism*
D006885:Hydroxybutyrates