{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,31]],"date-time":"2025-10-31T18:38:20Z","timestamp":1761935900295,"version":"build-2065373602"},"reference-count":23,"publisher":"Wiley","issue":"1","license":[{"start":{"date-parts":[[2009,2,3]],"date-time":"2009-02-03T00:00:00Z","timestamp":1233619200000},"content-version":"vor","delay-in-days":4051,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":["bpspubs.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["British J Pharmacology"],"published-print":{"date-parts":[[1998,1]]},"abstract":"<jats:p>\n<jats:list list-type=\"explicit-label\">\n<jats:list-item>\n<jats:p>The present work has examined the effects of short\u2010 (30\u2003min) and long\u2010term (14\u2003h) exposure to cyclosporine A (CsA) on the uptake of <jats:sc>L<\/jats:sc>\u2010DOPA, its decarboxylation to dopamine and the cellular extrusion of taken up <jats:sc>L<\/jats:sc>\u2010DOPA and of newly\u2010formed amine in monolayers of LLC\u2010PK<jats:sub>1<\/jats:sub> cells.<\/jats:p>\n<\/jats:list-item>\n<jats:list-item>\n<jats:p>In the presence of benserazide (50\u2003\u03bc<jats:sc>M<\/jats:sc>), <jats:sc>L<\/jats:sc>\u2010DOPA was rapidly accumulated in LLC\u2010PK<jats:sub>1<\/jats:sub> cells (cultured in collagen\u2010treated plastic) attaining equilibrium at 30\u2003min of incubation. Non\u2010linear analysis of the saturation curves revealed a <jats:italic>K<\/jats:italic><jats:sub>m<\/jats:sub> of 113\u00b116\u2003\u03bc<jats:sc>M<\/jats:sc> and a <jats:italic>V<\/jats:italic><jats:sub>max<\/jats:sub> of 5581\u00b1297\u2003pmol\u2003mg<jats:sup>\u22121<\/jats:sup> protein 6\u2003min<jats:sup>\u22121<\/jats:sup>.<\/jats:p>\n<\/jats:list-item>\n<jats:list-item>\n<jats:p>In the absence of benserazide, LLC\u2010PK<jats:sub>1<\/jats:sub> cells incubated with increasing concentrations of <jats:sc>L<\/jats:sc>\u2010DOPA (10 to 500\u2003\u03bc<jats:sc>M<\/jats:sc>) for 6\u2003min accumulate newly\u2010formed dopamine by a saturable process with apparent <jats:italic>K<\/jats:italic><jats:sub>m<\/jats:sub> and <jats:italic>V<\/jats:italic><jats:sub>max<\/jats:sub> values of 31\u00b16\u2003\u03bc<jats:sc>M<\/jats:sc> and 1793\u00b191\u2003pmol\u2003mg<jats:sup>\u22121<\/jats:sup> protein 6\u2003min<jats:sup>\u22121<\/jats:sup>, respectively. The fractional outflow of newly\u2010formed dopamine was found to be 20%. Up to 200\u2003\u03bc<jats:sc>M<\/jats:sc> of intracellular newly\u2010formed dopamine, the outward transfer of the amine was found to be a non\u2010saturable process.<\/jats:p>\n<\/jats:list-item>\n<jats:list-item>\n<jats:p>Short\u2010term exposure to CsA (0.3, 1.0 and 3.0\u2003\u03bcg\u2003ml<jats:sup>\u22121<\/jats:sup>) was found not to change the intracellular concentrations of newly\u2010formed dopamine, but increased the levels of dopamine in the incubation medium (143% to 224% increase) and the total amount of dopamine formed (31% to 59% increase). Long\u2010term exposure to CsA (0.03 to 3.0\u2003\u03bcg\u2003ml<jats:sup>\u22121<\/jats:sup>) reduced the total amount of dopamine (15% to 39% reduction) and the intracellular levels of the amine (11% to 56% reduction), without changing dopamine levels in the incubation medium. Both short\u2010 and long\u2010term exposure to CsA resulted in a concentration\u2010dependent increase in the fractional outflow of newly\u2010formed dopamine.<\/jats:p>\n<\/jats:list-item>\n<jats:list-item>\n<jats:p>Short\u2010term exposure to CsA (3.0\u2003\u03bcg\u2003ml<jats:sup>\u22121<\/jats:sup>) reduced the apical extrusion of intracellular <jats:sc>L<\/jats:sc>\u2010DOPA by 15% (<jats:italic>P<\/jats:italic>&lt;0.05), whereas long\u2010term exposure to CsA reverted this effect and decreased its intracellular availability (15% reduction; <jats:italic>P<\/jats:italic>&lt;0.05).<\/jats:p>\n<\/jats:list-item>\n<jats:list-item>\n<jats:p>Detection of P\u2010glycoprotein activity was carried out by measuring verapamil\u2010 or UIC2\u2010sensitive rhodamine 123 accumulation. Both UIC2 (3\u2003\u03bcg\u2003ml<jats:sup>\u22121<\/jats:sup>) and verapamil (25\u2003\u03bc<jats:sc>M<\/jats:sc>) significantly increased the accumulation of rhodamine 123 in LLC\u2010PK<jats:sub>1<\/jats:sub> cells. A 30\u2003min exposure to CsA was found not to affect the accumulation of rhodamine 123 in the presence of verapamil (25\u2003\u03bc<jats:sc>M<\/jats:sc>), whereas a 14\u2003h exposure to CsA was found to reduce the accumulation of rhodamine 123.<\/jats:p>\n<\/jats:list-item>\n<jats:list-item>\n<jats:p>In conclusion, the increase and the reduction in the formation of dopamine after short\u2010 and long\u2010term exposure to CsA, respectively, correlate with the effects of the immunosuppressant on the apical cell extrusion of taken up <jats:sc>L<\/jats:sc>\u2010DOPA, suggesting the involvement of P\u2010glycoprotein. The effects of CsA on the fractional outflow of newly\u2010formed dopamine appear to be mediated by a different mechanism.<\/jats:p>\n<\/jats:list-item>\n<\/jats:list>\n<\/jats:p><jats:p><jats:italic>British Journal of Pharmacology<\/jats:italic> (1998) <jats:bold>123<\/jats:bold>, 13\u201322; doi:<jats:ext-link xmlns:xlink=\"http:\/\/www.w3.org\/1999\/xlink\" ext-link-type=\"doi\" xlink:href=\"10.1038\/sj.bjp.0701572\">10.1038\/sj.bjp.0701572<\/jats:ext-link><\/jats:p>","DOI":"10.1038\/sj.bjp.0701572","type":"journal-article","created":{"date-parts":[[2005,1,28]],"date-time":"2005-01-28T19:14:07Z","timestamp":1106939647000},"page":"13-22","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["Evidence for the involvement of P\u2010glycoprotein on the extrusion of taken up <scp>L<\/scp>\u2010DOPA in cyclosporine A treated LLC\u2010PK<sub>1<\/sub> cells"],"prefix":"10.1111","volume":"123","author":[{"given":"P","family":"Soares\u2010da\u2010Silva","sequence":"first","affiliation":[]},{"given":"M P","family":"Serr\u00e3o","sequence":"additional","affiliation":[]},{"given":"M A","family":"Vieira\u2010Coelho","sequence":"additional","affiliation":[]},{"given":"M","family":"Pestana","sequence":"additional","affiliation":[]}],"member":"311","published-online":{"date-parts":[[2009,2,3]]},"reference":[{"key":"e_1_2_5_2_1","doi-asserted-by":"publisher","DOI":"10.1016\/0003-2697(76)90527-3"},{"key":"e_1_2_5_3_1","doi-asserted-by":"publisher","DOI":"10.1016\/0922-4106(90)90041-U"},{"key":"e_1_2_5_4_1","first-page":"1222","article-title":"Postnatal development of organic cation transport and MDR gene expression in mouse kidney","volume":"261","author":"Dutt A.","year":"1992","journal-title":"J. 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