{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,9]],"date-time":"2026-10-09T20:09:20Z","timestamp":1791576560673,"version":"4.3.4"},"reference-count":0,"publisher":"Rockefeller University Press","issue":"5","content-domain":{"domain":["rupress.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[1994,5,1]]},"abstract":"<jats:p>The renal medullary thick ascending limb (MTAL) actively reabsorbs ammonium ions. To examine the effects of NH4+ transport on intracellular pH (pHi) and the mechanisms of apical membrane NH4+ transport, MTALs from rats were isolated and perfused in vitro with 25 mM HCO3(-)-buffered solutions (pH 7.4). pHi was monitored using the fluorescent dye BCECF. In the absence of NH4+, the mean pHi was 7.16. Luminal addition of 20 mM NH4+ caused a rapid intracellular acidification (dpHi\/dt = 11.1 U\/min) and reduced the steady state pHi to 6.67 (delta pHi = 0.5 U), indicating that apical NH4+ entry was more rapid than entry of NH3. Luminal furosemide (10(-4) M) reduced the initial rate of cell acidification by 70% and the fall in steady state pHi by 35%. The residual acidification observed with furosemide was inhibited by luminal barium (12 mM), indicating that apical NH4+ entry occurred via both furosemide (Na(+)-NH4(+)-2Cl- cotransport) and barium-sensitive pathways. The role of these pathways in NH4+ absorption was assessed under symmetric ammonium conditions. With 4 mM NH4+ in perfusate and bath, mean steady state pHi was 6.61 and net ammonium absorption was 12 pmol\/min\/mm. Addition of furosemide to the lumen abolished net ammonium absorption and caused pHi to increase abruptly (dpHi\/dt = 0.8 U\/min) to 7.0. Increasing luminal [K+] from 4 to 25 mM caused a similar, rapid cell alkalinization. The pronounced cell alkalinization observed with furosemide or increasing [K+] was not observed in the absence of NH4+. In symmetric 4 mM NH4+ solutions, addition of barium to the lumen caused a slow intracellular alkalinization and reduced net ammonium absorption only by 14%. Conclusions: (a) ammonium transport is a critical determinant of pHi in the MTAL, with NH4+ absorption markedly acidifying the cells and maneuvers that inhibit apical NH4+ uptake (furosemide or elevation of luminal [K+]) causing intracellular alkalinization; (b) most or all of transcellular ammonium absorption is mediated by apical membrane Na(+)-NH4(+)-2Cl- cotransport; (c) NH4+ also permeates a barium-sensitive apical membrane transport pathway (presumably apical membrane K+ channels) but this pathway does not contribute significantly to ammonium absorption under physiologic (symmetric ammonium) conditions.<\/jats:p>","DOI":"10.1085\/jgp.103.5.917","type":"journal-article","created":{"date-parts":[[2004,5,13]],"date-time":"2004-05-13T23:51:34Z","timestamp":1084492294000},"page":"917-936","update-policy":"https:\/\/doi.org\/10.1085\/jgp.crossmarkpolicy","source":"Crossref","is-referenced-by-count":49,"title":["Effects of ammonium on intracellular pH in rat medullary thick ascending limb: mechanisms of apical membrane NH4+ transport."],"prefix":"10.1085","volume":"103","author":[{"suffix":"3rd","given":"B A","family":"Watts","sequence":"first","affiliation":[{"name":"Department of Internal Medicine, University of Texas Medical Branch, Galveston 77555-0562."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"D W","family":"Good","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine, University of Texas Medical Branch, Galveston 77555-0562."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"291","published-online":{"date-parts":[[1994,5,1]]},"container-title":["The Journal of general physiology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/rupress.org\/jgp\/article-pdf\/103\/5\/917\/1767948\/917.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/rupress.org\/jgp\/article-pdf\/103\/5\/917\/1767948\/917.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2023,7,26]],"date-time":"2023-07-26T10:37:16Z","timestamp":1690367836000},"score":1,"resource":{"primary":{"URL":"https:\/\/rupress.org\/jgp\/article\/103\/5\/917\/26384\/Effects-of-ammonium-on-intracellular-pH-in-rat"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1994,5,1]]},"references-count":0,"journal-issue":{"issue":"5","published-print":{"date-parts":[[1994,5,1]]}},"URL":"https:\/\/doi.org\/10.1085\/jgp.103.5.917","relation":{},"ISSN":["0022-1295","1540-7748"],"issn-type":[{"value":"0022-1295","type":"print"},{"value":"1540-7748","type":"electronic"}],"subject":[],"published":{"date-parts":[[1994,5,1]]}}}