{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T17:30:55Z","timestamp":1791307855743,"version":"4.3.1"},"reference-count":0,"publisher":"Rockefeller University Press","issue":"3","content-domain":{"domain":["rupress.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[1991,9,1]]},"abstract":"<jats:p>Measurements of the intracellular free concentration of Ca2+ ([Ca2+]i) were performed during fatiguing stimulation of intact, single muscle fibers, which were dissected from a mouse foot muscle and loaded with fura-2. Fatigue, which was produced by repeated 100-Hz tetani, generally occurred in three phases. Initially, tension declined rapidly to approximately 90% of the original tension (0.9 Po) and during this period the tetanic [Ca2+]i increased significantly (phase 1). Then followed a lengthy period of almost stable tension production and tetanic [Ca2+]i (phase 2). Finally, both the tetanic [Ca2+]i and tension fell relatively fast (phase 3). The resting [Ca2+]i rose continuously throughout the stimulation period. A 10-s rest period during phase 3 resulted in a significant increase of both tetanic [Ca2+]i and tension, whereas a 10-s pause during phase 2 did not have any marked effect. Application of caffeine under control conditions and early during phase 2 resulted in a substantial increase of the tetanic [Ca2+]i but no marked tension increase, whereas caffeine applied at the end of fatiguing stimulation (tension depressed to approximately 0.3 Po) gave a marked increase of both tetanic [Ca2+]i and tension. The tetanic [Ca2+]i for a given tension was generally higher during fatiguing stimulation than under control conditions. Fatigue developed more rapidly in fibers exposed to cyanide. In these fibers there was no increase of tetanic [Ca2+]i during phase 1 and the increase of the resting [Ca2+]i during fatiguing stimulation was markedly larger. The present results indicate that fatigue produced by repeated tetani is caused by a combination of reduced maximum tension-generating capacity, reduced myofibrillar Ca2+ sensitivity, and reduced Ca2+ release from the sarcoplasmic reticulum. The depression of maximum tension-generating capacity develops early during fatiguing stimulation and it is of greatest importance for the force decline at early stages of fatigue. As fatigue gets more severe, reduced Ca2+ sensitivity and reduced Ca2+ release become quantitatively more important for the tension decline.<\/jats:p>","DOI":"10.1085\/jgp.98.3.615","type":"journal-article","created":{"date-parts":[[2004,5,13]],"date-time":"2004-05-13T23:48:59Z","timestamp":1084492139000},"page":"615-635","update-policy":"https:\/\/doi.org\/10.1085\/jgp.crossmarkpolicy","source":"Crossref","is-referenced-by-count":310,"title":["Changes of myoplasmic calcium concentration during fatigue in single mouse muscle fibers."],"prefix":"10.1085","volume":"98","author":[{"given":"H","family":"Westerblad","sequence":"first","affiliation":[{"name":"Department of Physiology, University of Sydney, New South Wales, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"D G","family":"Allen","sequence":"additional","affiliation":[{"name":"Department of Physiology, University of Sydney, New South Wales, Australia."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"291","published-online":{"date-parts":[[1991,9,1]]},"container-title":["The Journal of general physiology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/rupress.org\/jgp\/article-pdf\/98\/3\/615\/1814649\/615.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/rupress.org\/jgp\/article-pdf\/98\/3\/615\/1814649\/615.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2023,7,27]],"date-time":"2023-07-27T12:37:34Z","timestamp":1690461454000},"score":1,"resource":{"primary":{"URL":"https:\/\/rupress.org\/jgp\/article\/98\/3\/615\/28046\/Changes-of-myoplasmic-calcium-concentration-during"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1991,9,1]]},"references-count":0,"journal-issue":{"issue":"3","published-print":{"date-parts":[[1991,9,1]]}},"URL":"https:\/\/doi.org\/10.1085\/jgp.98.3.615","relation":{},"ISSN":["0022-1295","1540-7748"],"issn-type":[{"value":"0022-1295","type":"print"},{"value":"1540-7748","type":"electronic"}],"subject":[],"published":{"date-parts":[[1991,9,1]]}}}