Uptake of L-leucine and L-phenylalanine across the basolateral cell surface in isolated oxyntic glands.
The time course, kinetic, specificity and sodium-dependence of L-leucine and L-phenylalanine uptake by rabbit isolated oxyntic glands were studied in order to identify the systems involved in the transport of branched-chain and aromatic neutral amino acids through the basolateral cell membrane. The uptake was measured directly in the disrupted cells after incubation of the glands with the 3H-labelled amino acid both in a sodium-containing and a sodium-free medium. The uptake of L-leucine was largely carrier-mediated whilst L-phenylalanine was taken up by either carrier-mediated and nonsaturable processes. Both amino acids were taken up by a Na(+)-independent process. The kinetic parameters of L-leucine and L-phenylalanine carrier-mediated influx were, respectively: Kt = 2.71 mM and Jmax = 1390 nmol mg-1 s-1, Kt = 1.03 mM and Jmax = 176 nmol mg-1 s-1. From cross-inhibition studies it can be inferred that L-leucine is primarily transported by a Na(+)-independent system which shows specificity for bulky side chains dipolar amino acids. The system displays similar affinities for L-phenylalanine (Ki = 2.81 mM) and L-isoleucine (Ki = 2.62 mM). Similar results were obtained from self-inhibition experiments: the Ki of the carrier-mediated uptake of L-leucine and L-phenylalanine were 2.12 and 2.40 mM (from a Hanes plot) or 3.2 and 0.8 mM (from a Dixon plot), respectively. It is concluded that a sodium-independent transport system, like Christensen's 'L' type, is shared by branched-chain and aromatic dipolar amino acids, which only shows slight differences in their affinities for the carrier.
Sobrevía
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Department of Physiological Sciences, Faculty of Biological Sciences and Natural Resources, University of Concepción, Chile.
Medina
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Reinicke
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Bravo
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I
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D066298:In Vitro Techniques; D007532:Isoleucine / Q000494:pharmacology; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D010295:Parietal Cells, Gastric / Q000378:metabolism*; D010649:Phenylalanine / Q000378:metabolism* / Q000494:pharmacology; D011817:Rabbits; D013395:Sucrose / Q000378:metabolism; D014316:Tritium
D007532:Isoleucine; D014316:Tritium; D010649:Phenylalanine; D013395:Sucrose; D007930:Leucine