{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,22]],"date-time":"2026-10-22T06:45:46Z","timestamp":1792651546823,"version":"4.5.0"},"reference-count":55,"publisher":"Wiley","issue":"2","license":[{"start":{"date-parts":[[2004,8,5]],"date-time":"2004-08-05T00:00:00Z","timestamp":1091664000000},"content-version":"vor","delay-in-days":1131,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["The Journal of Physiology"],"published-print":{"date-parts":[[2001,7]]},"abstract":"<jats:p>\n<jats:list list-type=\"explicit-label\">\n<jats:list-item><jats:p>The normal influence of heart rate (HR) on cardiac contraction and relaxation in the mouse remains uncertain despite its importance in interpreting many genetically engineered models. Prior <jats:italic>in vivo<\/jats:italic> data have repeatedly shown positive effects only at subphysiological heart rates, yet depressed basal conditions and use of load\u2010dependent parameters probably have an impact on these results.<\/jats:p><\/jats:list-item>\n<jats:list-item><jats:p>Open\u2010chest mice of various strains <jats:italic>(n =<\/jats:italic> 16, etomidate\/urethane anaesthesia) were instrumented with a miniaturized pressure\u2010volume catheter employing absolute left ventricular (LV) volume calibration. HR was slowed (&lt; 400 beats min<jats:sup>\u22121<\/jats:sup>) using ULFS\u201049, and atrial or ventricular pacing was achieved via an intra\u2010oesophageal catheter. Pressure\u2010volume data yielded cardiac\u2010specific contractile indexes minimally altered by vascular load.<\/jats:p><\/jats:list-item>\n<jats:list-item><jats:p>At a resting HR of 600 beats min<jats:sup>\u22121<\/jats:sup>, peak pressure\u2010rise rate (d<jats:italic>P<\/jats:italic>\/d<jats:italic>t<\/jats:italic><jats:sub>max<\/jats:sub>) was 16 871 \u00b1 2941 mmHg s<jats:sup>\u22121<\/jats:sup> (mean \u00b1<jats:sc>s.d<\/jats:sc>.) and the relaxation time constant was 3.9 \u00b1 0.8 ms, similar to values in conscious animals. Within the broad physiological range (500\u2010850 beats min<jats:sup>\u22121<\/jats:sup>), load\u2010insensitive contractile indexes and relaxation rate varied minimally, whereas d<jats:italic>P<\/jats:italic>\/d<jats:italic>t<\/jats:italic><jats:sub>max<\/jats:sub> peaked at 600 \u00b1 25 beats min<jats:sup>\u22121<\/jats:sup> and decreased at higher rates due to preload sensitivity. Contraction and relaxation were enhanced modestly (13\u201015 %) at HRs of between 400 and 500 beats min<jats:sup>\u22121<\/jats:sup>.<\/jats:p><\/jats:list-item>\n<jats:list-item><jats:p>The minimal force\u2010frequency dependence was explained by rapid calcium cycling kinetics, with a mechanical restitution time constant of 9 \u00b1 2.7 ms, and by dominant sarcoplasmic reticular buffering (recirculation fraction of 93 \u00b1 1 %).<\/jats:p><\/jats:list-item>\n<jats:list-item><jats:p>The mouse normally has a very limited force\u2010frequency reserve at physiological HRs, unlike larger mammals and man. This is important to consider when studying disease evolution and survival of genetic models that alter calcium homeostasis and SR function.<\/jats:p><\/jats:list-item>\n<\/jats:list>\n<\/jats:p>","DOI":"10.1111\/j.1469-7793.2001.00535.x","type":"journal-article","created":{"date-parts":[[2004,8,5]],"date-time":"2004-08-05T09:53:45Z","timestamp":1091699625000},"page":"535-545","source":"Crossref","is-referenced-by-count":118,"title":["Minimal force\u2010frequency modulation of inotropy and relaxation of <i>in situ<\/i> murine heart"],"prefix":"10.1113","volume":"534","author":[{"given":"Dimitrios","family":"Georgakopoulos","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David A.","family":"Kass","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2004,8,5]]},"reference":[{"key":"e_1_2_5_1_1","doi-asserted-by":"publisher","DOI":"10.1161\/01.RES.69.4.937"},{"key":"e_1_2_5_2_1","volume-title":"Excitation\u2010Contraction Coupling and Cardiac Contractile Force","author":"Bers D. 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