{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,13]],"date-time":"2026-05-13T15:23:14Z","timestamp":1778685794962,"version":"3.51.4"},"reference-count":0,"publisher":"Rockefeller University Press","issue":"6","content-domain":{"domain":["rupress.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[1978,6,1]]},"abstract":"<jats:p>Submaximum and maximum forces of the cardiac muscle contractile apparatus, activated by Ca2+ or Sr2+, were determined as a function of Mg2+ concentration. Apical left ventricular tissue from Sprague-Dawley rats was broken by homogenization into small bundles of fibers with disrupted sarcolemmas (skinned). Tension generation was activated by and graded according to the concentration of Ca2+ or Sr2+ in solutions bathing the skinned fibers and measured with a photodiode force transducer. Steady-state tensions for various levels of activation at each of four concentrations of Mg2+ (5 x 10(-5), 1 x 10(-3), 5 x 10(-3), and 10 x 10(-3) M) in the bathing solutions were analyzed. Other bathing solution constituents and parameters mimicked significant normal intracellular conditions while providing adequate buffering of [H+], [Ca2+], and [MgATP2-] (magnesium adenosine triphosphate). To assess changes in sensitivity of the mechanical system to activation by Ca2+ (or Sr2+), each submaximum tension was expressed as a percentage of the given fiber bundle's maximum force generated at saturating [Ca2+] (or [Sr2+]) at the same [Mg2+]. When plotted as saturation curves these data demonstrate that increasing [Mg2+] depresses Ca2+ sensitivity of the force-generating mechanism. The Ca2+ and Sr2+ sensitivity of the cardiac force-generating apparatus is similar at every [Mg2+], indicating that the magnitude of Mg2+ effect is similar for both types of activation. However, absolute maximum tensions at saturating activating cation concentration increased as [Mg2+] increased; the effect of Mg2+ on maximum force was proportionately the same for Ca2+ and Sr2+ activation. But because saturating [Ca2+] always resulted in a lower maximum force than saturating [Sr2+], this site of Ca2+-Mg2+ interaction appears distinct from the one influencing Ca2+ sensitivity.<\/jats:p>","DOI":"10.1085\/jgp.71.6.645","type":"journal-article","created":{"date-parts":[[2004,5,13]],"date-time":"2004-05-13T23:16:46Z","timestamp":1084490206000},"page":"645-655","update-policy":"https:\/\/doi.org\/10.1085\/jgp.crossmarkpolicy","source":"Crossref","is-referenced-by-count":31,"title":["Characterization of the effects of Mg2+ on Ca2+- and Sr2+-activated tension generation of skinned rat cardiac fibers."],"prefix":"10.1085","volume":"71","author":[{"given":"S K","family":"Donaldson","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"P M","family":"Best","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"G L","family":"Kerrick","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"291","published-online":{"date-parts":[[1978,6,1]]},"container-title":["The Journal of general physiology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/rupress.org\/jgp\/article-pdf\/71\/6\/645\/1811259\/645.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/rupress.org\/jgp\/article-pdf\/71\/6\/645\/1811259\/645.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2023,7,27]],"date-time":"2023-07-27T11:48:43Z","timestamp":1690458523000},"score":1,"resource":{"primary":{"URL":"https:\/\/rupress.org\/jgp\/article\/71\/6\/645\/26874\/Characterization-of-the-effects-of-Mg2-on-Ca2-and"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1978,6,1]]},"references-count":0,"journal-issue":{"issue":"6","published-print":{"date-parts":[[1978,6,1]]}},"URL":"https:\/\/doi.org\/10.1085\/jgp.71.6.645","relation":{},"ISSN":["0022-1295","1540-7748"],"issn-type":[{"value":"0022-1295","type":"print"},{"value":"1540-7748","type":"electronic"}],"subject":[],"published":{"date-parts":[[1978,6,1]]}}}