Effects of perturbation of the Na+ electrochemical gradient on influx and efflux of alanine in isolated rat hepatocytes.
Transmembrane alanine transport was studied in hepatocytes isolated from 48-h fasted rats. Aminooxyacetate was used to render alanine nonmetabolizable. Gramicidin D eliminated the transmembrane Na+ electrochemical gradient. At 135 mM Na+ and 0.1 mM alanine gramicidin D decreased the steady-state intracellular-to-extracellular alanine distribution ratio from 20.2 to 0.9. The underlying kinetic changes appeared to be a decrease in alanine influx to one-third of the control value and an increase in the rate constant of alanine efflux by a factor of 9. Analogous changes were observed when the Na+ gradient was decreased by ouabain. The inhibitory effect of gramicidin D on alanine influx was confined to the Na+-dependent, saturable component which showed a prominent increase in the apparent Km for alanine and a small decrease in the apparent Vmax. The effect of gramicidin D on alanine efflux was related to the increased cytosolic Na+ concentration: the rate constant of alanine efflux was increased by cytosolic Na+ with half-maximal stimulation at 30 mM; voltage-sensitive alanine efflux could not be demonstrated.
Kristensen
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Folke
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D000409:Alanine / Q000378:metabolism*; D000818:Animals; D004563:Electrochemistry; D005260:Female; D006096:Gramicidin / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
D006096:Gramicidin; D014634:Valinomycin; D010042:Ouabain; D012964:Sodium; D000409:Alanine