Heat acclimation and exercise training interact when combined in an overriding and trade-off manner: Physiologic-genomic linkage

Einat Kodesh, Nir Nesher, Assi Simaan, Benny Hochner, Ronen Beeri, Dan Gilon, Michael D. Stern, Gary Gerstenblith, Michal Horowitz

Research output: Contribution to journalArticlepeer-review


Combined heat acclimation (AC) and exercise training (EX) enhance exercise performance in the heat while meeting thermoregulatory demands. We tested the hypothesis that different stress-specific adaptations evoked by each stressor individually trigger similar cardiac alterations, but when combined, overriding/trade-off interactions take place. We used echocardiography, isolated cardiomyocyte imaging and cDNA microarray techniques to assay in situ cardiac performance, excitationcontraction (EC) coupling features, and transcriptional programs associated with cardiac contractility. Rat groups studied were controls (sedentary 24°C); AC (sedentary, 34°C, 1 mo); normothermic EX (treadmill at 24°C, 1 mo); and heat-acclimated, exercise-trained (EXAC; treadmill at 34°C, 1 mo). Prolonged heat exposure decreased heart rate and contractile velocity and increased end ventricular diastolic diameter. Compared with controls, AC/EXAC cardiomyocytes demonstrated lower L-type Ca 2+ current (ICaL) amplitude, higher Ca 2+ transient (Ca 2+T), and a greater Ca 2+T-to-I CaL ratio; EX alone enhanced I CaL and Ca 2+T, whereas aerobic training in general induced cardiac hypertrophy and action potential elongation in EX/ EXAC animals. At the genomic level, the transcriptome profile indicated that the interaction between AC and EX yields an EXACspecific molecular program. Genes affected by chronic heat were linked with the EC coupling cascade, whereas aerobic training upregulated genes involved with Ca 2+ turnover via an adrenergic/ metabolic-driven positive inotropic response. In the EXAC cardiac phenotype, the impact of chronic heat overrides that of EX on EC coupling components and heart rate, whereas EX regulates cardiac morphometry. We suggest that concerted adjustments induced by AC and EX lead to enhanced metabolic and mechanical performance of the EXAC heart.

Original languageEnglish
Pages (from-to)R1786-R1797
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number6
StatePublished - Dec 2011
Externally publishedYes


  • Ca sup signaling
  • Echocardiography
  • Genomic responses
  • Isolated cardiomyocytes

ASJC Scopus subject areas

  • Physiology (medical)
  • Physiology


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