title: Hypothermia/rewarming disrupts excitation-contraction coupling in cardiomyocytes.
abstract: Hypothermia/rewarming (H/R) is poorly tolerated by the myocardium; however, the underlying intracellular basis of H/R-induced cardiac dysfunction remains elusive. We hypothesized that in cardiomyocytes, H/R disrupts excitation-contraction coupling by reducing myofilament Ca(2+) sensitivity due to an increase in cardiac troponin I (cTnI) phosphorylation. To test this hypothesis, isolated rat cardiomyocytes (13-15 cells from 6 rats per group) were electrically stimulated to evoke both cytosolic Ca(2+) ([Ca(2+)]cyto) and contractile (sarcomere shortening) responses that were simultaneously measured using an IonOptix system. Cardiomyocytes were divided into two groups: 1) those exposed to hypothermia (15°C for 2 h) followed by rewarming (35°C; H/R); or 2) time-matched normothermic (35°C) controls (CTL). Contractile dysfunction after H/R was indicated by reduced velocity and extent of sarcomere length (SL) shortening compared with time-matched controls. Throughout hypothermia, basal [Ca(2+)]cyto increased and the duration of evoked [Ca(2+)]cyto transients was prolonged. Phase-loop plots of [Ca(2+)]cyto vs. contraction were shifted rightward in cardiomyocytes during hypothermia compared with CTL, indicating a decrease in Ca(2+) sensitivity. Using Western blot, we found that H/R increases cTnI phosphorylation. These results support our overall hypothesis and suggest that H/R disrupts excitation-contraction coupling of cardiomyocytes due to increased cTnI phosphorylation and reduced Ca(2+) sensitivity.
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and.
authors.forename: Niccole
authors.initials: N
authors.lastname: Schaible
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and.
authors.forename: Young Soo
authors.initials: YS
authors.lastname: Han
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and.
authors.forename: Thuy
authors.initials: T
authors.lastname: Hoang
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and.
authors.forename: Grace
authors.initials: G
authors.lastname: Arteaga
authors.affiliation: Departments of Anesthesiology and Physiology, University of Tromsø-The Arctic University of Norway, Tromsø, Norway.
authors.forename: Torkjel
authors.initials: T
authors.lastname: Tveita
authors.affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota; and Sieck.Gary@mayo.edu.
authors.forename: Gary
authors.initials: G
authors.lastname: Sieck
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002304:Cardiac Pacing, Artificial; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D056966:Excitation Contraction Coupling; D007036:Hypothermia, Induced / Q000009:adverse effects*; D008297:Male; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010766:Phosphorylation; D017207:Rats, Sprague-Dawley; D017694:Rewarming / Q000009:adverse effects*; D012518:Sarcomeres / Q000378:metabolism; D013997:Time Factors; D019210:Troponin I / Q000378:metabolism
chemical_list: D019210:Troponin I; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium
keywords: cardiomyocyte; excitation-contraction coupling; hypothermia; rewarming; troponin I