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      Acute Regulation of the Betaine/GABA Transporter BGT-1 Expressed in Xenopus Oocytes by Extracellular pH

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          Abstract

          Besides uptake of Na<sup>+</sup> and Cl<sup>–</sup>, mammalian cells counteract osmotic cell shrinkage also by Na<sup>+</sup>-coupled uptake of osmolytes, e.g., myo-inositol, taurine or betaine. The expression of the corresponding transporters is transcriptionally regulated by the ambient pH and osmolarity and is increased upon cell shrinkage, a process requiring hours. The present study has been performed to disclose rapid regulation by pH of osmolyte transport via BGT-1. Transport of GABA was investigated by using the two-electrode voltage-clamp technique with BGT-1 expressing Xenopus oocytes. GABA was used as a substrate, because of the low oocyte endogenous transport activity. Extracellular acidification to pH 5.5 reversibly decreased and extracellular alkalinization to pH 8.5 increased GABA-induced currents. Kinetic analysis revealed that extracellular alkalinization increases the affinity for Cl<sup>–</sup> as reflected by a decrease of the apparent K<sub>m</sub>-value for Cl<sup>–</sup> from >500 m M to 55.8 ± 4.7 m M upon an increase of the pH from 7.0 to 8.5. The apparent K<sub>m</sub>- values for Na<sup>+</sup> and GABA remained unaltered in the pH range from 6.0 to 8.5. Instead, alkalinization increased the maximal current induced by saturating Na<sup>+</sup> and GABA concentrations. The results are compatible with a model of interference of H<sup>+</sup> ions with Cl<sup>–</sup> binding and a pH-dependent reduction of V<sub>max</sub> for Na<sup>+</sup> and GABA.

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          Most cited references 5

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          The Diversity of Volume Regulatory Mechanisms

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            Swelling-activated organic osmolyte channels.

             K. Kirk Shung (1997)
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              Functional Characterization of the Betaine/γ-Aminobutyric Acid Transporter BGT-1 Expressed inXenopusOocytes

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                Author and article information

                Journal
                KBR
                Kidney Blood Press Res
                10.1159/issn.1420-4096
                Kidney and Blood Pressure Research
                S. Karger AG
                1420-4096
                1423-0143
                2000
                2000
                02 November 2000
                : 23
                : 6
                : 356-359
                Affiliations
                aDepartment of Physiology, University of Tübingen, Germany; bSechenov Institute of Comparative Physiology and Biochemistry, St. Petersburg, Russia; cInstitute for Cellular Signaling, University of Nijmegen, The Netherlands
                Article
                25983 Kidney Blood Press Res 2000;23:356–359
                10.1159/000025983
                11070414
                © 2000 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 3, References: 26, Pages: 4
                Product
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/25983
                Categories
                Original Paper

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