{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T21:35:50Z","timestamp":1774474550329,"version":"3.50.1"},"reference-count":0,"publisher":"American Physiological Society","issue":"1","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["American Journal of Physiology-Cell Physiology"],"published-print":{"date-parts":[[1989,1,1]]},"abstract":"<jats:p> The high level of ascorbic acid (AA) in the aqueous humor of many mammals suggests an active transport of AA across the double-layered ciliary epithelium from blood to aqueous humor. We used [14C]AA to study AA uptake in bovine pigmented ciliary epithelial cells in tissue culture. We observed a 40-fold intracellular accumulation of AA, which was dependent on extracellular Na+. With labeled dehydroascorbate (DHA, the oxidized form of the vitamin) in the medium, there was a 20-fold intracellular accumulation of the label. However, the time course of DHA uptake was different compared with AA uptake and was not Na+ dependent, suggesting different transport systems for AA and DHA. AA uptake was inhibited by 1 mM phloretin and in the presence of isoascorbate. Furthermore, AA uptake was markedly reduced when intracellular Na+ was elevated by preincubation with ouabain or amphotericin B. With increasing AA concentration, Na+-dependent AA uptake exhibited first-order saturation kinetics with half-maximal uptake at 76 microM AA. Na+ dependence of AA uptake revealed a sigmoidal curve of Na+-dependent AA uptake vs. Na+ concentration with a half-maximal AA uptake at 45.4 mM Na+. The slope of the Hill plot from these data was 1.94, suggesting a transport system translocating two or more Na+ for one AA. This stoichiometry implies electrogenicity of the transporter. We, therefore, measured membrane potentials using conventional microelectrodes. Addition of 200 microM AA resulted in a depolarization of the membrane voltage by 4.9 +\/- 0.5 mV (n = 22), which was absent in Na+ free medium and was markedly reduced by phloretin.(ABSTRACT TRUNCATED AT 250 WORDS) <\/jats:p>","DOI":"10.1152\/ajpcell.1989.256.1.c44","type":"journal-article","created":{"date-parts":[[2017,12,24]],"date-time":"2017-12-24T15:12:28Z","timestamp":1514128348000},"page":"C44-C49","source":"Crossref","is-referenced-by-count":72,"title":["Electrogenic Na+-ascorbate cotransport in cultured bovine pigmented ciliary epithelial cells"],"prefix":"10.1152","volume":"256","author":[{"given":"H.","family":"Helbig","sequence":"first","affiliation":[{"name":"Institut fur Klinische Physiologie, Klinikum Steglitz der FreienUniversitat Berlin, Federal Republic of Germany."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"C.","family":"Korbmacher","sequence":"additional","affiliation":[{"name":"Institut fur Klinische Physiologie, Klinikum Steglitz der FreienUniversitat Berlin, Federal Republic of Germany."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"J.","family":"Wohlfarth","sequence":"additional","affiliation":[{"name":"Institut fur Klinische Physiologie, Klinikum Steglitz der FreienUniversitat Berlin, Federal Republic of Germany."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"S.","family":"Berweck","sequence":"additional","affiliation":[{"name":"Institut fur Klinische Physiologie, Klinikum Steglitz der FreienUniversitat Berlin, Federal Republic of Germany."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"D.","family":"Kuhner","sequence":"additional","affiliation":[{"name":"Institut fur Klinische Physiologie, Klinikum Steglitz der FreienUniversitat Berlin, Federal Republic of Germany."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"M.","family":"Wiederholt","sequence":"additional","affiliation":[{"name":"Institut fur Klinische Physiologie, Klinikum Steglitz der FreienUniversitat Berlin, Federal Republic of Germany."}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"24","container-title":["American Journal of Physiology-Cell Physiology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/journals.physiology.org\/doi\/pdf\/10.1152\/ajpcell.1989.256.1.C44","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2024,6,17]],"date-time":"2024-06-17T19:49:43Z","timestamp":1718653783000},"score":1,"resource":{"primary":{"URL":"https:\/\/journals.physiology.org\/doi\/10.1152\/ajpcell.1989.256.1.C44"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1989,1,1]]},"references-count":0,"journal-issue":{"issue":"1","published-print":{"date-parts":[[1989,1,1]]}},"alternative-id":["10.1152\/ajpcell.1989.256.1.C44"],"URL":"https:\/\/doi.org\/10.1152\/ajpcell.1989.256.1.c44","relation":{},"ISSN":["0363-6143","1522-1563"],"issn-type":[{"value":"0363-6143","type":"print"},{"value":"1522-1563","type":"electronic"}],"subject":[],"published":{"date-parts":[[1989,1,1]]}}}