{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,20]],"date-time":"2026-02-20T22:22:35Z","timestamp":1771626155898,"version":"3.50.1"},"reference-count":0,"publisher":"Wiley","issue":"3","license":[{"start":{"date-parts":[[1973,2,1]],"date-time":"1973-02-01T00:00:00Z","timestamp":97372800000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["The Journal of Physiology"],"published-print":{"date-parts":[[1973,2]]},"abstract":"<jats:p>1. Cardiac sarcoplasmic reticulum (SR) was prepared by differential centrifugation from euthyroid, hyperthyroid, hypothyroid as well as <jats:sup>131<\/jats:sup>I\u2010treated plus thyroxine\u2010substituted rabbits. The function of the isolated SR has been characterized by measuring the ATP\u2010dependent calcium uptake, the calcium storing capacity, the calcium concentrating ability and the calcium\u2010dependent ATP hydrolysis by the calcium\u2010activated ATPase in the presence of oxalate.<\/jats:p><jats:p>2. The rate of calcium uptake and the rate of the calcium\u2010dependent ATP hydrolysis (calcium\u2010activated ATPase) by the SR were significantly increased in hyperthyroidism, whilst both activities were markedly reduced in hypothyroidism. Thyroxine administration to <jats:sup>131<\/jats:sup>I\u2010treated animals prevented a decrease in the rate of calcium uptake as well as in the rate of the calcium\u2010dependent ATP hydrolysis by the calcium\u2010activated ATPase.<\/jats:p><jats:p>3. The transport ratio (rate of calcium uptake divided by the rate of calcium\u2010dependent ATP hydrolysis) of SR preparations from euthyroid controls was 0\u00b793, suggesting a stoicheiometry of calcium uptake and calcium\u2010activated ATP split of 1\u00b70. The transport ratio was unchanged in one hyper\u2010 and hypothyroid group, whilst a small but significant decrease or increase was observed after an excessive thyroxine treatment of a prolonged state of hypothyroidism, respectively.<\/jats:p><jats:p>4. The saturation kinetics of calcium transport by the SR were described by Michaelis\u2014Menten kinetics. The maximum rate of calcium uptake (<jats:italic>V<\/jats:italic>) was 0\u00b7193\u00b10\u00b7004, 0\u00b7223\u00b10\u00b7002 and 0\u00b7124\u00b10\u00b7003 \u03bcmole Ca<jats:sup>2+<\/jats:sup>\/mg protein. min (means \u00b1S.E.) for euthyroid, hyperthyroid and hypothyroid SR, respectively. The Michaelis constants (<jats:italic>K<jats:sub>m<\/jats:sub><\/jats:italic>) were (2\u00b787\u00b10\u00b730) \u00d7 10<jats:sup>\u22127<\/jats:sup> \n<jats:sc>M<\/jats:sc> (2\u00b768\u00b10\u00b715) \u00d7 10<jats:sup>\u22127<\/jats:sup> \n<jats:sc>M<\/jats:sc> and (4\u00b700\u00b10\u00b748) \u00d7 10<jats:sup>\u22127<\/jats:sup> \n<jats:sc>M<\/jats:sc> for the euthyroid, hyperthyroid and hypothyroid SR, respectively (means \u00b1S.E.). The <jats:italic>K<jats:sub>m<\/jats:sub><\/jats:italic> values for the hyper\u2010 and hypothyroid SR were not significantly different from controls.<\/jats:p><jats:p>5. The calcium storing capacity as well as the calcium concentrating ability of the SR was unaltered at different levels of thyroid activity.<\/jats:p><jats:p>6. The steady\u2010state level of calcium was the same for SR isolated from euthyroid, hyperthyroid and hypothyroid rabbits, indicating that calcium influx and calcium efflux are strongly coupled at steady\u2010state filling of the SR.<\/jats:p><jats:p>7. It is suggested that the increased or reduced rate of calcium transport by the SR in hyperthyroidism or hypothyroidism, respectively, found <jats:italic>in vitro<\/jats:italic>, might be at least partially responsible for the shortening of the relaxation time of cardiac muscle in the hyperthyroid state and the prolongation of the relaxation time in the hypothyroid state observed <jats:italic>in vitro<\/jats:italic> and <jats:italic>in vivo<\/jats:italic>.<\/jats:p>","DOI":"10.1113\/jphysiol.1973.sp010100","type":"journal-article","created":{"date-parts":[[2014,12,19]],"date-time":"2014-12-19T10:31:37Z","timestamp":1418985097000},"page":"563-582","source":"Crossref","is-referenced-by-count":97,"title":["The calcium pump of cardiac sarcoplasmic reticulum. Functional alterations at different levels of thyroid state in rabbits"],"prefix":"10.1113","volume":"228","author":[{"given":"J.","family":"Suko","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[1973,2]]},"container-title":["The Journal of Physiology"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/api.wiley.com\/onlinelibrary\/tdm\/v1\/articles\/10.1113%2Fjphysiol.1973.sp010100","content-type":"unspecified","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/physoc.onlinelibrary.wiley.com\/doi\/pdf\/10.1113\/jphysiol.1973.sp010100","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2023,11,8]],"date-time":"2023-11-08T20:48:32Z","timestamp":1699476512000},"score":1,"resource":{"primary":{"URL":"https:\/\/physoc.onlinelibrary.wiley.com\/doi\/10.1113\/jphysiol.1973.sp010100"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1973,2]]},"references-count":0,"journal-issue":{"issue":"3","published-print":{"date-parts":[[1973,2]]}},"alternative-id":["10.1113\/jphysiol.1973.sp010100"],"URL":"https:\/\/doi.org\/10.1113\/jphysiol.1973.sp010100","archive":["Portico"],"relation":{},"ISSN":["0022-3751","1469-7793"],"issn-type":[{"value":"0022-3751","type":"print"},{"value":"1469-7793","type":"electronic"}],"subject":[],"published":{"date-parts":[[1973,2]]}}}