title: Atrioventricular nodal reverse facilitation in connexin40-deficient mice.
abstract: BACKGROUND
  Facilitation is an important physiologic property of the atrioventricular (AV) node. Previous studies demonstrated abnormal AV conduction in connexin (Cx)40-deficient mice.
  
  
  OBJECTIVE
  We hypothesize that Cx40-deficient mice display altered patterns of AV nodal facilitation compared with wild-type mice.
  
  
  METHODS
  Sixteen 36-week-old mice (eight Cx40(-/-) mice and eight Cx40(+/+) controls) underwent in vivo closed chest electrophysiologic study. A 2Fr octapolar catheter was advanced into the right ventricle to record a His-bundle electrogram. A special facilitation stimulation protocol was performed in each mouse to evaluate facilitation. Following atrial drive pacing (S1S1) at 150 ms, a facilitating beat S2 was delivered prior to the test beat S3. S3H3 was measured for varying S1S2 values at fixed H2S3 intervals.
  
  
  RESULTS
  Progressive shortening of S1S2 (from 150 ms to 130, 110, and 90 ms) resulted in gradual prolongation of S2H2. The prolongation was more pronounced in Cx40(-/-) mice for each S1S2 compared with wild-type mice (P <.001). In each wild-type mouse, for a given H2S3 interval, this gradual increase in S2H2 produced progressive shortening of S3H3, so-called AV nodal facilitation phenomenon. However, in each Cx40(-/-) mouse, facilitation was seen only at S1S2 of 130 ms (P <.001 vs S1S2 of 150 ms). Evidence of reverse facilitation was documented at S1S2 of 110 and 90 ms.
  
  
  CONCLUSIONS
  Facilitation is observed in wild-type mice. With similar S1S2 intervals in Cx40-deficient mice, facilitation is seen only at longer S1S2 intervals, whereas reverse facilitation is seen at shorter S1S2 intervals, suggesting that Cx40 is involved in the generation of AV nodal facilitation.
authors.affiliation: Cardiac Arrhythmia Service, New England Medical Center, Boston, MA, USA. wei.zhu@sickkids.ca
authors.forename: Wei
authors.initials: W
authors.lastname: Zhu
authors.forename: Samir
authors.initials: S
authors.lastname: Saba
authors.forename: Mark S
authors.initials: MS
authors.lastname: Link
authors.forename: Eugene
authors.initials: E
authors.lastname: Bak
authors.forename: Munther K
authors.initials: MK
authors.lastname: Homoud
authors.forename: N A Mark
authors.initials: NA
authors.lastname: Estes
authors.forename: David L
authors.initials: DL
authors.lastname: Paul
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Wang
mesh_terms: D000818:Animals; D001283:Atrioventricular Node / Q000502:physiology*; D002036:Bundle of His / Q000502:physiology; D002304:Cardiac Pacing, Artificial; D017630:Connexins / Q000172:deficiency*; D017629:Gap Junctions / Q000378:metabolism; D006339:Heart Rate / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008839:Microelectrodes; D015398:Signal Transduction / Q000502:physiology; D000097003:Gap Junction alpha-5 Protein
chemical_list: D017630:Connexins; D000097003:Gap Junction alpha-5 Protein