Alpha actin isoforms expression in human and rat adult cardiac conduction system.
In the adult heart, cardiac muscle comprises the working myocardium and the conduction system (CS). The latter includes the sinoatrial node (SAN), the internodal tract or bundle (IB), the atrioventricular node (AVN), the atrioventricular bundle (AVB), the bundle branches (BB) and the peripheral Purkinje fibers (PF). Most of the information concerning the phenotypic features of CS tissue derives from the characterization of avian and rodent developing hearts; data concerning the expression of actin isoforms in adult CS cardiomyocytes are scarce. Using specific antibodies, we investigated the distribution of alpha-skeletal (alpha-SKA), alpha-cardiac (alpha-CA), alpha-smooth muscle (alpha-SMA) actin isoforms and other muscle-typical proteins in the CS of human and rat hearts at different ages. SAN and IB cardiomyocytes were characterized by the presence of alpha-SMA, alpha-CA, calponin and caldesmon, whereas alpha-SKA and vimentin were absent. Double immunofluorescence demonstrated the co-localisation of alpha-SMA and alpha-CA in I-bands of SAN cardiomyocytes. AVN, AVB, BB and PF cardiomyocytes were alpha-SMA, calponin, caldesmon and vimentin negative, and alpha-CA and alpha-SKA positive. No substantial differences in actin isoform distribution were observed in human and rat hearts, except for the presence of isolated subendocardial alpha-SMA positive cardiomyocytes co-expressing alpha-CA in the ventricular septum of the rat. Aging did not influence CS cardiomyocyte actin isoform expression profile. These findings support the concept that cardiomyocytes of SAN retain the phenotype of a developing myogenic cell throughout the entire life span.
Orlandi
Augusto
A
Institute of Anatomic Pathology, Department of Biopathology and Image Diagnostics, Tor Vergata University of Rome-PTV, Via Montpellier 1, 00133, Rome, Italy. orlandi@uniroma2.it
Hao
Hiroyuki
H
Ferlosio
Amedeo
A
Clément
Sophie
S
Hirota
Seiichi
S
Spagnoli
Luigi Giusto
LG
Gabbiani
Giulio
G
Chaponnier
Christine
C
D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D002478:Cells, Cultured; D005260:Female; D005786:Gene Expression Regulation; D006329:Heart Conduction System / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D032383:Myocytes, Cardiac / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D012849:Sinoatrial Node / Q000378:metabolism; D055815:Young Adult
D000199:Actins; D020033:Protein Isoforms