Redistribution of connexin45 in gap junctions of connexin43-deficient hearts.
OBJECTIVE
Adult ventricular myocytes express two gap junction channel proteins: connexin43 (Cx43) and connexin45 (Cx45). Cx43-deficient mice exhibit slow ventricular epicardial conduction, suggesting that Cx43 plays an important role in intercellular coupling in the ventricle. Cx45 is much less abundant than Cx43 in working ventricular myocytes. Its role in ventricular conduction has not been defined, nor is it known whether expression or distribution of Cx45 is altered in Cx43-deficient mice. The present study was undertaken to determine (1) whether expression of Cx45 is upregulated and (2) whether gap junction structure and distribution are altered in Cx43-deficient mice.


METHODS
Ventricular tissue from neonatal Cx43(+/+), Cx43(+/-) and Cx43(-/-) and adult Cx43(+/+) and Cx43(+/-) mice was analyzed by immunoblotting and confocal immunofluorescence microscopy.


RESULTS
Total Cx45 protein abundance measured by immunoblotting was not different in Cx43-deficient or null hearts compared to wild-type control hearts. However, the amount and distribution of Cx45 immunoreactive signal measured by quantitative confocal analysis were markedly reduced in both Cx43(+/-) and Cx43(-/-) hearts.


CONCLUSIONS
Although the total content of Cx45 is not upregulated in Cx43-deficient hearts, the localization of Cx45 to cardiac gap junctions depends on the expression level of Cx43 and is dramatically altered in mice that express no Cx43.
Johnson
Carolyn M
CM
Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.
Kanter
Evelyn M
EM
Green
Karen G
KG
Laing
James G
JG
Betsuyaku
Tetsuo
T
Beyer
Eric C
EC
Steinberg
Thomas H
TH
Saffitz
Jeffrey E
JE
Yamada
Kathryn A
KA
D000818:Animals; D000831:Animals, Newborn; D018031:Connexin 43 / Q000378:metabolism; D017630:Connexins / Q000172:deficiency / Q000378:metabolism*; D017629:Gap Junctions / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009206:Myocardium / Q000378:metabolism*; D000097003:Gap Junction alpha-5 Protein
D018031:Connexin 43; D017630:Connexins; D000097003:Gap Junction alpha-5 Protein; C082920:connexin 45