Differential activation of system A and betaine/GABA transport in MDCK cell membranes by hypertonic stress.
Biochim Biophys Acta
; 1372(1): 117-23, 1998 Jun 24.
Article
em En
| MEDLINE
| ID: mdl-9651499
ABSTRACT
Accumulation of osmolytes by renal cells is due in part to increased uptake via specific transporters. These include amino acid transport system A and the betaine/GABA transporter (BGT1). Transport changes have been characterized using intact cells which makes the intracellular mechanisms difficult to determine. In this study the hypertonic upregulation of system A and BGT1 was studied directly at the membrane level in Madin-Darby canine kidney (MDCK) cells. Both system A and BGT1 transport systems were detected in an isolated membrane fraction containing plasma membranes. System A transport was increased in membranes prepared from cells after 6 h hypertonic stress (449 mosmol/kg) but BGT1 activity was minimal and not different from isotonic controls. The increase in system A was blocked by inhibitors of RNA and protein synthesis. BGT1 transport was induced in membranes prepared after 24 h hypertonicity. At this time system A activity in the membrane fraction remained increased, unlike the downregulation observed in intact MDCK cells. We conclude that differential upregulation of system A and BGT1 by hypertonic stress is due to intrinsic changes in these transporters at the membrane level. In contrast, the downregulation of system A in intact cells when hypertonicity is prolonged for 24 h is likely due to the action of an intracellular repressor that is not present in the isolated membranes.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Estresse Fisiológico
/
Betaína
/
Aminoacilação de RNA de Transferência
/
Ácido gama-Aminobutírico
Limite:
Animals
Idioma:
En
Ano de publicação:
1998
Tipo de documento:
Article