Transmural distribution of connexins in rodent hearts.
BACKGROUND
Electrophysiologic heterogeneity across the ventricular wall is a result of differential transmural expression of various ion channel proteins that underlie the different action potential waveforms observed in epicardial, midmyocardial, and endocardial regions. Cardiac connexins mediate cell-to-cell communication, are critical for normal impulse propagation, and play a role in electrophysiologic remodeling in disease states. However, little is known about the transmural distribution of cardiac gap junction proteins.


RESULTS
Connexin expression in epicardium, midmyocardium, and endocardium was assessed immunohistochemically in mouse and rat hearts. The total connexin protein content within different ventricular regions was measured by immunoblotting. Connexin43 is twice as abundant in midmyocardium and endocardium compared with epicardium in the mouse but not in the rat. Connexin45 is expressed equally across the left ventricular wall.


CONCLUSIONS
Epicardial myocytes express significantly less Cx43 and therefore may be less well coupled than midmyocardial and endocardial myocytes. A transmural gradient of connexin43 expression across the left ventricular free wall likely results in differences in the stoichiometry of connexins expressed in different regions of the heart.
Yamada
Kathryn A
KA
Department of Medicine(Cardiovascular Division), Washington University School of Medicine, St. Louis, Missouri 63110, USA. kyamada@im.wustl.edu
Kanter
Evelyn M
EM
Green
Karen G
KG
Saffitz
Jeffrey E
JE
D000818:Animals; D018031:Connexin 43 / Q000378:metabolism*; D017630:Connexins / Q000378:metabolism; D022062:Electrophysiologic Techniques, Cardiac; D004699:Endocardium / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006352:Heart Ventricles / Q000378:metabolism; D015151:Immunoblotting; D051379:Mice; D008810:Mice, Inbred C57BL; D023421:Models, Animal; D008955:Models, Cardiovascular; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012377:Rodentia
D018031:Connexin 43; D017630:Connexins; C082920:connexin 45