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      Naloxone Inhibits A6 Cell Na +/H + Exchange by Activating Protein Kinase C via the Mobilization of Intracellular Calcium

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          Abstract

          The opioid receptor antagonist, naloxone, has been shown to have beneficial effects in the kidney and to be implicated in renal salt and water balance. In the present study the signal transduction pathways utilized by naloxone were studied in an epithelial cell line model of the cortical collecting duct, A6 cells. We found that naloxone has a dual effect depending on the concentration used: at a low concentration (10<sup>–6</sup> M) it antagonized the β-endorphin-dependent increase in cytoplasmic calcium [Ca<sup>2+</sup>]<sub>i</sub>, while at higher concentrations (>10<sup>–5</sup> M) it increased [Ca<sup>2+</sup>]<sub>i</sub> and intracellular inositol phosphate levels. While naloxone-induced increases in [Ca<sup>2+</sup>]<sub>i</sub> occurred in the absence of external calcium, it was significantly stimulated by increasing the external calcium concentration, suggesting that naloxone increases [Ca<sup>2+</sup>]<sub>i</sub> via both calcium release and calcium influx. In polarized A6 cell monolayers naloxone inhibited the activity of the Na<sup>+</sup>/H<sup>+</sup> exchanger (NHE) only when added to the basolateral cell surface. This inhibition of the NHE was prevented by pretreatment of the cells with either the intracellular calcium chelator, BAPTA or with the protein kinase C inhibitor, calphostin C. These findings demonstrate that naloxone induces a rapid increase in intracellular calcium which inhibits the NHE via the calcium-dependent protein kinase C regulatory pathway.

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          Most cited references 4

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          On the specificity of naloxone as an opiate antagonist.

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            A capacitative calcium current in cultured skeletal muscle cells is mediated by the calcium-specific leak channel and inhibited by dihydropyridine compounds.

            Calcium stores from cultured skeletal muscle cells were depleted using cyclopiazonic acid (CPA), a reversible inhibitor of Ca2+-ATPases at the sarcoplasmic reticulum. Store depletion led to activation of the calcium-specific leak channel, as assayed using single-channel patch clamp analysis and rates of manganese influx and quenching of fura-2 fluorescence. Two novel dihydropyridine compounds inhibited this single-channel leak channel activity, the resting and depletion-induced manganese influx, and refilling of the CPA-depleted intracellular calcium store. These compounds represent the first antagonists for a calcium leak channel and for a channel that mediates a capacitative current. The development of the skeletal muscle capacitative current was inhibited by genistein, a tyrosine kinase inhibitor, but was not affected by okadaic acid, a phosphatase inhibitor, or econazole. Thus, the capacitative current in cultured skeletal muscle cells was mediated by the calcium leak channel and was inhibited by pharmacological antagonists and may provide a model system for uncovering the complete set of signals leading from store depletion to channel activation.
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              Proteolysis of the human platelet and endothelial cell thrombin receptor by neutrophil-derived cathepsin G

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                Author and article information

                Journal
                EXN
                Nephron Exp Nephrol
                10.1159/issn.1660-2129
                Cardiorenal Medicine
                S. Karger AG
                1660-2129
                2001
                2001
                31 August 2001
                : 9
                : 5
                : 341-348
                Affiliations
                aDepartment of General and Environmental Physiology and bDepartment of Animal Production, Section of Reproduction, University of Bari, Italy
                Article
                52630 Exp Nephrol 2001;9:341–348
                10.1159/000052630
                11549852
                © 2001 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: 6, References: 40, Pages: 8
                Product
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/52630
                Categories
                Original Paper

                Cardiovascular Medicine, Nephrology

                Na+/H+ exchanger, Renal calcium, Naloxone

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