title: Up-regulation of connexin45 in heart failure.
abstract: BACKGROUND
  Heart failure is associated with reduced expression of the major gap junction protein connexin43 (Cx43), which may contribute to arrhythmias and sudden cardiac death in this patient population. Other cardiac connexins may be altered as well. Because connexin45 (Cx45) has been shown to colocalize with Cx43, we determined whether the number, size, or distribution of Cx45 gap junctions is altered in the failing heart.
  
  
  RESULTS
  Cx45 expression levels were measured by immunoblotting and quantitative immunostaining in failing and control human left ventricles. Total Cx45 protein was significantly (P = 0.021) up-regulated 1.8-fold in failing hearts. Cx45 immunohistochemical signal was increased by 80% (P = 0.005) due to a 3.5-fold increase in the number of gap junctions containing Cx45. Cx45 mRNA was not altered in failing hearts, suggesting reduced degradation of Cx45 protein in the failing heart. Cx43 signal, on the other hand, was reduced by 49% in failing hearts. Double-label experiments demonstrated colocalization of Cx45 and Cx43 in the same gap junctions.
  
  
  CONCLUSIONS
  Cx45 is markedly enhanced in the failing heart. Up-regulation of Cx45 in conjunction with down-regulation of Cx43 could result in abnormal impulse propagation and generation of ventricular arrhythmias, thereby predisposing patients in heart failure to sudden cardiac death.
authors.affiliation: Department of Medicine (Cardiovascular Division), Center for Cardiovascular Research, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA. kyamada@im.wustl.edu
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Yamada
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Rogers
authors.forename: Rune
authors.initials: R
authors.lastname: Sundset
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Steinberg
authors.forename: Jeffrey  E
authors.initials: J
authors.lastname: Saffitz
mesh_terms: D000328:Adult; D018031:Connexin 43 / Q000378:metabolism*; D017630:Connexins / Q000378:metabolism*; D005260:Female; D006333:Heart Failure / Q000150:complications / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D015854:Up-Regulation; D018487:Ventricular Dysfunction, Left / Q000209:etiology / Q000378:metabolism*
chemical_list: D018031:Connexin 43; D017630:Connexins; C082920:connexin 45