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Neutral amino acid transport mediated by ortholog of imino acid transporter SIT1/SLC6A20 in opossum kidney cells

Neutral amino acid transport mediated by ortholog of imino acid transporter SIT1/SLC6A20 in... Most neutral L -amino acid acids are transported actively across the luminal brush-border membrane of small intestine and kidney proximal tubule epithelial cells by a Na + cotransport system named B 0 that has been recently molecularly identified (B 0 AT1, SLC6A19 ). We show here that the opossum kidney-derived cell line OK also displays a Na + -dependent B 0 -type neutral L -amino acid transport, although with a slightly differing substrate selectivity. We tested the hypothesis that one of the two B 0 AT1-related transporters, SLC6A18 (ortholog of orphan transporter XT2) or SLC6A20 (ortholog of the recently identified mammalian imino acid transporter SIT1), mediates this transport. Anti-sense RNA to OK SIT1 ( o SIT1) but not to OK XT2 ( o XT2) inhibited Na + -dependent neutral amino acid transport induced by OK mRNA injected in Xenopus laevis oocytes. Furthermore, inhibition of o SIT1 gene expression in OK cells by transfection of siRNA and expression of shRNA selectively reduced the Na + -dependent uptake of neutral L -amino acids. Finally, expression of OK cell o SIT1 cRNA in X. laevis oocytes induced besides the transport of the L -imino acid L -Pro also that of neutral L -amino acids. Taken together, the data indicate that in OK cells SIT1 (SLC6A20) is not only an apical imino acid transporter but also plays a major role as Na + -dependent neutral L -amino acid transporter. A similar double role could be envisaged for SIT1 in mammalian kidney proximal tubule and small intestine. Na + -dependent neurotransmitter transporter; B 0 AT1; Xenopus laevis oocytes; kidney proximal tubule; anti-sense; siRNA Address for reprint requests and other correspondence: F. Verrey, Institute of Physiology, Univ. of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland (e-mail: verrey@access.unizh.ch ) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png AJP - Renal Physiology The American Physiological Society

Neutral amino acid transport mediated by ortholog of imino acid transporter SIT1/SLC6A20 in opossum kidney cells

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Publisher
The American Physiological Society
Copyright
Copyright © 2011 the American Physiological Society
ISSN
0363-6127
eISSN
1522-1466
DOI
10.1152/ajprenal.00319.2005
pmid
16234310
Publisher site
See Article on Publisher Site

Abstract

Most neutral L -amino acid acids are transported actively across the luminal brush-border membrane of small intestine and kidney proximal tubule epithelial cells by a Na + cotransport system named B 0 that has been recently molecularly identified (B 0 AT1, SLC6A19 ). We show here that the opossum kidney-derived cell line OK also displays a Na + -dependent B 0 -type neutral L -amino acid transport, although with a slightly differing substrate selectivity. We tested the hypothesis that one of the two B 0 AT1-related transporters, SLC6A18 (ortholog of orphan transporter XT2) or SLC6A20 (ortholog of the recently identified mammalian imino acid transporter SIT1), mediates this transport. Anti-sense RNA to OK SIT1 ( o SIT1) but not to OK XT2 ( o XT2) inhibited Na + -dependent neutral amino acid transport induced by OK mRNA injected in Xenopus laevis oocytes. Furthermore, inhibition of o SIT1 gene expression in OK cells by transfection of siRNA and expression of shRNA selectively reduced the Na + -dependent uptake of neutral L -amino acids. Finally, expression of OK cell o SIT1 cRNA in X. laevis oocytes induced besides the transport of the L -imino acid L -Pro also that of neutral L -amino acids. Taken together, the data indicate that in OK cells SIT1 (SLC6A20) is not only an apical imino acid transporter but also plays a major role as Na + -dependent neutral L -amino acid transporter. A similar double role could be envisaged for SIT1 in mammalian kidney proximal tubule and small intestine. Na + -dependent neurotransmitter transporter; B 0 AT1; Xenopus laevis oocytes; kidney proximal tubule; anti-sense; siRNA Address for reprint requests and other correspondence: F. Verrey, Institute of Physiology, Univ. of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland (e-mail: verrey@access.unizh.ch )

Journal

AJP - Renal Physiology – The American Physiological Society

Published: Apr 1, 2006

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