EFFECTS OF PH ON BETA-HYDROXYBUTYRATE TRANSPORT IN RAT ERYTHROCYTES AND THYMOCYTES

Entry of β-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 α-cyanocinnamate. We studied the dependence of influx and efflux on internal and external pH and [β-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 β-hydroxybutyrate enhanced efflux slightly. At high external pH, external β-hydroxybutyrate inhibited efflux. Internal acidification inhibited influx and internal alkalization enhanced influx. Internal β-hydroxybutyrate (βHB) enhanced influx more in acidified than alkalized cells. These data are compatible with coupled βHB-/OH- exchange, βHB- and OH- competing for influx, C : OH- moving faster than C : βHB-, empty C being immobile. They are also compatible with coupled βHB-/H+ copermeation, empty C moving inward faster than H+ : C : βHB-, H+ : C being immobile, and C : βHB- (without H+) being so unstable as not to be formed in significant amounts (relative to C, H+ : C, and H+ : C : βHB-). © 1978.