{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,27]],"date-time":"2026-09-27T14:23:14Z","timestamp":1790518994541,"version":"4.1.0"},"reference-count":32,"publisher":"Rockefeller University Press","issue":"5","content-domain":{"domain":["rupress.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2014,5,1]]},"abstract":"<jats:p>The mating call of the Atlantic toadfish is generated by bursts of high-frequency twitches of the superfast twitch fibers that surround the swimbladder. At 16\u00b0C, a calling period can last several hours, with individual 80\u2013100-Hz calls lasting \u223c500 ms interleaved with silent periods (intercall intervals) lasting \u223c10 s. To understand the intracellular movements of Ca2+ during the intercall intervals, superfast fibers were microinjected with fluo-4, a high-affinity fluorescent Ca2+ indicator, and stimulated by trains of 40 action potentials at 83 Hz, which mimics fiber activity during calling. The fluo-4 fluorescence signal was measured during and after the stimulus trains; the signal was also simulated with a kinetic model of the underlying myoplasmic Ca2+ movements, including the binding and transport of Ca2+ by the sarcoplasmic reticulum (SR) Ca2+ pumps. The estimated total amount of Ca2+ released from the SR during a first stimulus train is \u223c6.5 mM (concentration referred to the myoplasmic water volume). At 40 ms after cessation of stimulation, the myoplasmic free Ca2+ concentration ([Ca2+]) is below the threshold for force generation (\u223c3 \u00b5M), yet the estimated concentration of released Ca2+ remaining in the myoplasm (\u0394[CaM]) is large, \u223c5 mM, with \u223c80% bound to parvalbumin. At 10 s after stimulation, [Ca2+] is \u223c90 nM (three times the assumed resting level) and \u0394[CaM] is \u223c1.3 mM, with 97% bound to parvalbumin. Ca2+ movements during the intercall interval thus appear to be strongly influenced by (a) the accumulation of Ca2+ on parvalbumin and (b) the slow rate of Ca2+ pumping that ensues when parvalbumin lowers [Ca2+] near the resting level. With repetitive stimulus trains initiated at 10-s intervals, Ca2+ release and pumping come quickly into balance as a result of the stability (negative feedback) supplied by the increased rate of Ca2+ pumping at higher [Ca2+].<\/jats:p>","DOI":"10.1085\/jgp.201411160","type":"journal-article","created":{"date-parts":[[2014,4,15]],"date-time":"2014-04-15T03:27:34Z","timestamp":1397532454000},"page":"605-620","update-policy":"https:\/\/doi.org\/10.1085\/jgp.crossmarkpolicy","source":"Crossref","is-referenced-by-count":10,"title":["Intracellular calcium movements during relaxation and recovery of superfast muscle fibers of the toadfish swimbladder"],"prefix":"10.1085","volume":"143","author":[{"given":"Frank E.","family":"Nelson","sequence":"first","affiliation":[{"name":"Department of Biology 1 and 2"},{"name":"Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104 1 and 2"},{"name":"Whitman Center, The Marine Biological Laboratory, Woods Hole, MA 02543 3"},{"name":"Department of Biology, Temple University, Philadelphia, PA 19122 4"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stephen","family":"Hollingworth","sequence":"additional","affiliation":[{"name":"Department of Biology 1 and 2"},{"name":"Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104 1 and 2"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lawrence C.","family":"Rome","sequence":"additional","affiliation":[{"name":"Department of Biology 1 and 2"},{"name":"Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104 1 and 2"},{"name":"Whitman Center, The Marine Biological Laboratory, Woods Hole, MA 02543 3"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stephen M.","family":"Baylor","sequence":"additional","affiliation":[{"name":"Department of Biology 1 and 2"},{"name":"Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104 1 and 2"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"291","published-online":{"date-parts":[[2014,4,14]]},"reference":[{"key":"2023072623180656400_bib1","doi-asserted-by":"publisher","first-page":"543","DOI":"10.1007\/BF01738442","article-title":"Quantitation of Ca ATPase, feet and mitochondria in superfast muscle fibres from the toadfish, Opsanus tau","volume":"12","author":"Appelt","year":"1991","journal-title":"J. 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