Molecular identification of p-glycoprotein: a role in lens circulation?

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dc.contributor.author Merriman-Smith, Barbara en
dc.contributor.author Young, MA en
dc.contributor.author Jacobs, MD en
dc.contributor.author Kistler, Joerg en
dc.contributor.author Donaldson, Paul en
dc.date.accessioned 2011-09-05T00:40:03Z en
dc.date.issued 2002 en
dc.identifier.citation INVEST OPHTH VIS SCI 43(9):3008-3015 Sep 2002 en
dc.identifier.issn 0146-0404 en
dc.identifier.uri http://hdl.handle.net/2292/7650 en
dc.description.abstract PURPOSE. To determine whether P-glycoprotein is expressed in the rat lens and to assess what type of damage occurs when P-glycoprotein inhibitors are applied to organ-cultured lenses. METHODS. An initial screening for the P-glycoprotein isoforms multidrug resistance (mdr)1a, mdr1b, and mdr2 was performed by RT-PCR on RNA extracted from rat lens fiber cells. Northern blot analysis was used to determine whether transcript levels detected by RT-PCR were significant. The presence of P-glycoprotein in the lens was confirmed by Western blot analysis and immunocytochemistry. Organ-cultured lenses, maintained in isotonic artificial aqueous humor, were exposed to various concentrations of the P-glycoprotein inhibitor tamoxifen. Lens opacification was assessed by dark-field microscopy, and the underlying cellular changes were visualized by confocal microscopy of lens sections, using a fluorescent membrane marker. Initial cellular damage was assessed after a 6-hour exposure to 100 μM tamoxifen. Other P-glycoprotein inhibitors, verapamil, and 1,9-dideoxyforskolin (DDFK) were assessed, and the damage phenotypes were compared with those seen for tamoxifen. RESULTS. Transcript for all three P-glycoprotein isoforms was detected with RT-PCR, but only mdr1a and mdr2 could be detected by Northern blot analysis. P-glycoprotein was localized in the plasma membrane of lens epithelial and fiber cells. Treatment of organ-cultured lenses with increasing doses of the P-glycoprotein inhibitor tamoxifen for 18 hours showed that two distinct damage phenotypes were evident. At a dose of 20 μM tamoxifen, tissue damage was found in a discrete zone that initially started approximately 100 μm from the capsule, whereas at higher doses (60–100 μM tamoxifen), extensive vesiculation of fiber cell membranes occurred throughout the entire lens cortex. Decreasing tamoxifen (100 μM) exposure to 6 hours showed that the inner zone of damage was caused by the dilation of extracellular space between fiber cells. The extracellular space dilution and fiber cell vesiculation could be reproduced by varying the concentrations of other P-glycoprotein inhibitors, verapamil and DDKF. CONCLUSIONS. The P-glycoproteins mdr1a and mdr2 are expressed in the lens and appear to be functional. The initial cellular damage phenotype of extracellular space dilations caused by the P-glycoprotein inhibitors was identical with that caused by chloride channel inhibitors, indicating that P-glycoprotein may play a role in regulating cell volume in the lens. Whether the secondary damage phenotype of fiber cell vesiculation, induced by high doses of P-glycoprotein inhibitors, was due to the inhibition of additional regulatory activities of P-glycoprotein or to nonspecific effects of the drugs remains to be determined. However, regardless of the precise mode of action, these results indicate that P-glycoprotein should be considered in the regulatory mechanisms associated with the control of lens volume and in the initiation of osmotic cataract. en
dc.description.uri http://www.iovs.org/cgi/content/abstract/43/9/3008 en
dc.language EN en
dc.relation.ispartofseries Investigative Ophthalmology & Visual Science en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. Details obtained from http://www.sherpa.ac.uk/romeo/issn/0146-0404/ en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.subject ACTIVATED CHLORIDE CHANNELS en
dc.subject MDR GENE FAMILY en
dc.subject MULTIDRUG-RESISTANCE en
dc.subject RAT LENS en
dc.subject DISINTEGRATIVE GLOBULIZATION en
dc.subject VOLUME REGULATION en
dc.subject TRANSGENIC MICE en
dc.subject CATARACT en
dc.subject CELLS en
dc.subject CLONING en
dc.title Molecular identification of p-glycoprotein: a role in lens circulation? en
dc.type Journal Article en
pubs.issue 9 en
pubs.begin-page 3008 en
pubs.volume 43 en
dc.rights.holder Copyright: Association for Research in Vision and Ophthalmology en
pubs.end-page 3015 en
dc.rights.accessrights http://purl.org/eprint/accessRights/RestrictedAccess en
pubs.subtype Article en
pubs.elements-id 57604 en
pubs.org-id Bioengineering Institute en
pubs.org-id ABI Associates en
pubs.org-id Medical and Health Sciences en
pubs.org-id Medical Sciences en
pubs.org-id Science en
pubs.org-id Science Research en
pubs.org-id Maurice Wilkins Centre (2010-2014) en
pubs.record-created-at-source-date 2010-09-01 en
pubs.dimensions-id 12202523 en


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