Influence of rBAT-mediated amino acid transport on cytosolic pH.
rBAT, together with its subunit b(0,+) AT mediates the hetero- and homoexchange of neutral and dibasic amino acids. Since the heteroexchange of dibasic amino acids against neutral amino acids is coupled to net transport of positive charge, this transport is electrogenic. Extracellular addition of histidine could create an inward or an outward current depending on extracellular pH (pH(e)) and cell membrane potential. It has been concluded that histidine may be transported in both its protonated and its neutral form. In this study measurements of cytosolic pH (pH(i)) were performed to test this hypothesis. As a result, addition of protonated histidine at acidic pH(e) to Xenopus oocytes expressing rBAT creates an inward current which is paralleled by cytosolic acidification. Both can be reduced by increase of pH(e). At alkaline pH(e) and simultaneous depolarization of the cell membrane the effect of histidine on pH(i) is virtually abolished. The neutral amino acid leucine does not alter cytosolic pH at neither pH 6.0 nor at pH 8.0. In conclusion, histidine can be transported in either its neutral or its protonated form. Transport of the protonated form is facilitated by extracellular acidification and hyperpolarization of the cell membrane.
Department of Physiology, University of Tübingen, Germany.
Ivano
I
Moschèn
Iwan
I
Setiawan
Manuel
M
Palacin
Stefan
S
Bröer
Alexandra
A
Albers
Florian
F
Lang
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels; D008565:Membrane Proteins / Q000502:physiology*; D024101:Mitochondrial Proteins; D011994:Recombinant Proteins / Q000378:metabolism; D000071256:Uncoupling Protein 1; D014982:Xenopus laevis
D000596:Amino Acids; D002352:Carrier Proteins; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D011994:Recombinant Proteins; D000071256:Uncoupling Protein 1