title: Electrophysiological mechanisms of antiarrhythmic protection during hypothermia in winter hibernating versus nonhibernating mammals.
abstract: BACKGROUND
  Robust cell-to-cell coupling is critically important in the safety of cardiac conduction and protection against ventricular fibrillation (VF). Hibernating mammals have evolved naturally protective mechanisms against VF induced by hypothermia and reperfusion injury.
  
  
  OBJECTIVE
  We hypothesized that this protection strategy involves a dynamic maintenance of conduction and repolarization patterns through the improvement of gap junction functions.
  
  
  METHODS
  We optically mapped the hearts of summer-active (SA) and winter-hibernating (WH) ground squirrels Spermophilus undulatus from Siberia and nonhibernating rabbits during different temperatures (+3 degrees C to +37 degrees C).
  
  
  RESULTS
  Midhypothermia (+17 degrees C) resulted in nonuniform conduction slowing, increased dispersion of repolarization, shortened wavelength, and consequently enhanced VF induction in SA ground squirrels and rabbits. In contrast, wavelength was increased during hypothermia in WH hearts in which VF was not inducible at any temperature. In SA and rabbit hearts, but not in WH, conduction anisotropy was significantly increased by pacing acceleration, thus promoting VF induction during hypothermia. WH hearts maintained the same rate-independent anisotropic propagation pattern even at 3 degrees C. connexin 43 (Cx43) had more homogenous transmural distribution in WH ventricles as compared to SA. Moreover, Cx43 and N-cadherins (N-cad) densities as well as the percentage of their colocalization were significantly higher in WH compared to SA epicardium.
  
  
  CONCLUSIONS
  Rate-independent conduction anisotropy ratio, low dispersion of repolarization, and long wavelength-these are the main electrophysiological mechanisms of antiarrhythmic protection in hibernating mammalian species during hypothermia. This strategy includes the improved gap junction function, which is due to overexpression and enhanced colocalization of Cx43 and N-cad.
authors.affiliation: Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130-4899, USA. vadimfed@gmail.com
authors.forename: Vadim V
authors.initials: VV
authors.lastname: Fedorov
authors.forename: Alexey V
authors.initials: AV
authors.lastname: Glukhov
authors.forename: Sangita
authors.initials: S
authors.lastname: Sudharshan
authors.forename: Yuri
authors.initials: Y
authors.lastname: Egorov
authors.forename: Leonid V
authors.initials: LV
authors.lastname: Rosenshtraukh
authors.forename: Igor R
authors.initials: IR
authors.lastname: Efimov
mesh_terms: D000818:Animals; D001145:Arrhythmias, Cardiac / Q000503:physiopathology* / Q000517:prevention & control; D022062:Electrophysiologic Techniques, Cardiac; D006329:Heart Conduction System / Q000502:physiology*; D006605:Hibernation / Q000502:physiology*; D007035:Hypothermia; D008322:Mammals; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology*; D011817:Rabbits; D012589:Sciuridae