{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,2]],"date-time":"2025-11-02T19:21:03Z","timestamp":1762111263693},"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>This study is concerned with the regulation of intracellular-free Mg2+ concentration ([Mg2+]i) in the smooth muscle of guinea pig taenia caeci. To assess an interaction of Ca2+ on the Na(+)-dependent Mg(2+)-extrusion mechanism (Na(+)-Mg2+ exchange), effects of Na+ removal (N-methyl-D-glucamine substitution) were examined in Ca(2+)-containing solutions. As changes in pHi in Na(+)-free solutions perturb estimation of [Mg2+]i using the single chemical shift only of the beta-ATP peak in 31P NMR (nuclear magnetic resonance) spectra, [Mg2+]i and pHi were concomitantly estimated from the chemical shifts of the gamma- and beta-peaks. When extracellular Na+ was substituted with N-methyl-D-glucamine, [Mg2+]i was reversibly increased. This increase in [Mg2+]i was eliminated in Mg(2+)-free solutions and enhanced in excess Mg2+ solutions. ATP content fluctuated little during removal and readmission of Na+, indicating that [Mg2+]i changes were not induced by Mg2+ release from ATP, and that Mg(2+)-extruding system would not be inhibited by fuel restriction. A slow acidification in Na(+)-free solutions and transient alkalosis by a readmission of Na+ were observed regardless of the extracellular Mg2+ concentration. When the extracellular Ca2+ concentration was increased from normal (2.4 mM) to 12 mM, only a marginal increase in [Mg2+]i was caused by Na+ removal, whereas a similar slow acidosis was observed, indicating that extracellular Ca2+ inhibits Mg2+ entry, and that the increase in [Mg2+]i is negligible through competition between Mg2+ and Ca2+ in intracellular sites. These results imply that Na(+)-Mg2+ exchange is the main mechanism to maintain low [Mg2+]i even under physiological conditions.<\/jats:p>","DOI":"10.1085\/jgp.103.5.833","type":"journal-article","created":{"date-parts":[[2004,5,13]],"date-time":"2004-05-13T23:51:34Z","timestamp":1084492294000},"page":"833-851","update-policy":"http:\/\/dx.doi.org\/10.1085\/jgp.crossmarkpolicy","source":"Crossref","is-referenced-by-count":15,"title":["Intracellular-free magnesium in the smooth muscle of guinea pig taenia caeci: a concomitant analysis for magnesium and pH upon sodium removal."],"prefix":"10.1085","volume":"103","author":[{"given":"S","family":"Nakayama","sequence":"first","affiliation":[{"name":"University Department of Pharmacology, Oxford, UK."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"H","family":"Nomura","sequence":"additional","affiliation":[{"name":"University Department of Pharmacology, Oxford, UK."}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"T","family":"Tomita","sequence":"additional","affiliation":[{"name":"University Department of Pharmacology, Oxford, UK."}],"role":[{"role":"author","vocabulary":"crossref"}]}],"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\/833\/1767946\/833.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/rupress.org\/jgp\/article-pdf\/103\/5\/833\/1767946\/833.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2023,7,26]],"date-time":"2023-07-26T10:37:12Z","timestamp":1690367832000},"score":1,"resource":{"primary":{"URL":"https:\/\/rupress.org\/jgp\/article\/103\/5\/833\/26387\/Intracellular-free-magnesium-in-the-smooth-muscle"}},"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.103.5.833","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]]}}}