{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,23]],"date-time":"2026-09-23T01:09:02Z","timestamp":1790125742037,"version":"4.0.1"},"reference-count":39,"publisher":"American Physiological Society","issue":"1","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Journal of Applied Physiology"],"published-print":{"date-parts":[[2007,7]]},"abstract":"<jats:p>Heat acclimation (AC) improves cardiac mechanical and metabolic performance. Using cardiomyocytes and isolated hearts from 30-day and 2-day acclimated rats (AC and AC-2d, 34\u00b0C), we characterized cellular contractile mechanisms under normothermic (37\u00b0C) and hyperthermic (39\u201342\u00b0C) conditions. To determine contractile responses, Ca<jats:sup>2+<\/jats:sup>transients (Ca<jats:sup>2+<\/jats:sup>T), sarcoplasmic reticulum (SR) Ca<jats:sup>2+<\/jats:sup>pool size (fura-2\/indo-1 fluorescence), force generation [amplitude systolic motion (ASM)], L-type Ca<jats:sup>2+<\/jats:sup>channels [dihydropyridine receptor (DHPR)], ryanodine receptors (RyRs), and total (PLBt) and phosphorylated phospholamban [serine phosphorylated (PLBs) and theonine phosphorylated (PLBtr)] proteins and transcripts were measured (Western blot, RT-PCR). Cardiac mechanical performance was measured using a Langendorff system. We demonstrated that AC and AC-2d increased Ca<jats:sup>2+<\/jats:sup>T amplitude (148% and 147%, respectively) and twitch force (180% and 130%, respectively) and desensitized myofilaments, as indicated by a rightward shift in the ASM-Ca<jats:sup>2+<\/jats:sup>relationships, despite no change in SR Ca<jats:sup>2+<\/jats:sup>pool size. Hence, generation of higher Ca<jats:sup>2+<\/jats:sup>T underlies greater force development in AC and AC-2d myocytes. In isolated hearts, ryanodine administration eliminated differences between AC and control (C) hearts, implying an important role for RyRs in that acclimation phase. Increased expression of DHPR and RyRs, and decreased PLBs\/PLBt in AC hearts only, suggest that different pathways increase force generation in the AC-2d vs. AC myocytes. At basal beating rates, hyperthermia (39\u201341\u00b0C) enhanced pressure generation in AC hearts. C hearts failed to restitute pressure beyond 39\u00b0C. Increased beating frequency produced negative inotropic response. In C cardiomyocytes, hyperthermia elevated basal cytosolic Ca<jats:sup>2+<\/jats:sup>and tension, Ca<jats:sup>2+<\/jats:sup>T, and ASM. AC myocytes enhanced Ca<jats:sup>2+<\/jats:sup>T but showed myofilament desensitization, suggesting its involvement in cardiac protection against hyperthermia. Collectively, both Ca<jats:sup>2+<\/jats:sup>turnover and myofilament responsiveness are important adaptive acclimatory targets during normothermic and hyperthermic conditions.<\/jats:p>","DOI":"10.1152\/japplphysiol.01351.2006","type":"journal-article","created":{"date-parts":[[2007,3,30]],"date-time":"2007-03-30T01:04:20Z","timestamp":1175216660000},"page":"266-275","source":"Crossref","is-referenced-by-count":30,"title":["Altered Ca<sup>2+<\/sup>handling and myofilament desensitization underlie cardiomyocyte performance in normothermic and hyperthermic heat-acclimated rat hearts"],"prefix":"10.1152","volume":"103","author":[{"given":"Omer","family":"Cohen","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hifa","family":"Kanana","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ronen","family":"Zoizner","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chaya","family":"Gross","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Uri","family":"Meiri","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michael D.","family":"Stern","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gary","family":"Gerstenblith","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michal","family":"Horowitz","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"24","reference":[{"key":"R1","doi-asserted-by":"publisher","DOI":"10.1161\/01.RES.69.2.266"},{"key":"R2","doi-asserted-by":"crossref","unstructured":"Arieli Y, Kaspler P, Horowitz M.Chronic exposure to different ambient temperatures affects \u03b2AR profile and heart responsiveness to isoproterenol and calcium.Isr J Zool49: 219\u2013231, 2003.","DOI":"10.1560\/DTRB-NLUJ-0EMP-N0K4"},{"key":"R3","doi-asserted-by":"publisher","DOI":"10.1152\/physiol.00019.2006"},{"key":"R4","doi-asserted-by":"publisher","DOI":"10.1196\/annals.1380.015"},{"key":"R5","doi-asserted-by":"publisher","DOI":"10.1152\/ajpcell.1993.264.6.C1587"},{"key":"R6","doi-asserted-by":"publisher","DOI":"10.1074\/jbc.M004079200"},{"key":"R7","doi-asserted-by":"publisher","DOI":"10.1111\/j.1432-1033.2004.04332.x"},{"key":"R8","doi-asserted-by":"publisher","DOI":"10.1046\/j.1540-8167.2001.00563.x"},{"key":"R9","doi-asserted-by":"publisher","DOI":"10.1152\/ajpregu.2000.279.1.R77"},{"key":"R10","doi-asserted-by":"publisher","DOI":"10.1152\/ajpregu.1999.276.2.R550"},{"key":"R11","doi-asserted-by":"publisher","DOI":"10.1152\/ajprenal.1983.245.1.F1"},{"key":"R12","doi-asserted-by":"publisher","DOI":"10.1007\/BF00512465"},{"key":"R13","doi-asserted-by":"publisher","DOI":"10.1126\/science.276.5313.800"},{"key":"R14","doi-asserted-by":"publisher","DOI":"10.1152\/ajpcell.1997.273.1.C37"},{"key":"R15","doi-asserted-by":"crossref","unstructured":"Grynkiewicz G, Poenie M, Tsien RY.A new generation of Ca2+indicators with greatly improved fluorescence properties.J Biol Chem260: 3440\u20133450, 1985.","DOI":"10.1016\/S0021-9258(19)83641-4"},{"key":"R16","doi-asserted-by":"publisher","DOI":"10.1042\/BST0340232"},{"key":"R17","doi-asserted-by":"publisher","DOI":"10.1152\/japplphysiol.01244.2005"},{"key":"R18","doi-asserted-by":"crossref","unstructured":"Horowitz M.Do cellular heat acclimation responses modulate central thermoregulatory activity?News Physiol Sci13: 218\u2013225, 1998.","DOI":"10.1152\/physiologyonline.1998.13.5.218"},{"key":"R19","doi-asserted-by":"publisher","DOI":"10.1016\/S1095-6433(01)00500-1"},{"key":"R20","unstructured":"Horowitz M.Matching the heart to heat-induced circulatory load: heat-acclimatory responses.News Physiol Sci18: 215\u2013221, 2003."},{"key":"R21","doi-asserted-by":"publisher","DOI":"10.1016\/S0022-2828(86)80916-6"},{"key":"R22","unstructured":"Kodesh E, Nesher N, Hochner B, Horowitz M.Cardiac adaptation to heat and exercise training: molecular-physiological linkage in force generation (Abstract). 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