title: Differential gene expression and regulation of angiotensin II receptor subtypes in rat cardiac fibroblasts and cardiomyocytes in culture.
abstract: Although both rat cardiac nonmyocytes (mostly fibroblasts) and cardiomyocytes have a functional angiotensin II (AngII) receptor, the regulation mechanism of its subtype expression in the rat heart remains unknown. In this study, by using a binding assay and a competitive reverse-transcriptase polymerase chain reaction, we examined the regulation of AngII types 1a and 1b (AT1a-R and AT1b-R) and type 2 receptor (AT2-R) expression in embryonal day 19 (E19) and neonatal (1-d) rat cardiac fibroblasts and cardiomyocytes. The number of AT2-R in E19 fibroblasts was dramatically decreased (from 305 to 41 fmol/mg protein) in 1-d fibroblasts, whereas that of AT1-R and the mRNA levels remained unchanged. The ratio of AT1a-R to AT1b-R mRNA in both E19 and 1-d fibroblasts was 9:1. The number of AT2-R in E19 cardiomyocytes was also significantly decreased (from 178 to 87 fmol/mg protein) in 1-d cardiomyocytes, whereas the magnitude was less prominent compared with that in fibroblasts. AT1-R expression remained unaltered in E19 and 1-d cardiomyocytes. In E19 and 1-d cardiomyocytes, the AT1b-R mRNA level was 1.5-fold higher than that of AT1a-R mRNA. Dexamethasone induced significant increases in AT1a-R mRNA (2.1-fold) and numbers (1.8-fold) without changing the affinity, whereas neither AT1b-R mRNA nor the number of AT2-R was affected by dexamethasone. The AT1a-R gene transcription rate, determined by means of a nuclear run-off assay, was increased (2-fold) by dexamethasone. The half-life of AT1a-R mRNA (18 h) was unchanged by dexamethasone. These data indicate that AngII receptor subtype expression in the rat heart is regulated in a cell- and subtype-specific manner.
authors.affiliation: Second Department of Internal Medicine, Kansai Medical University, Osaka, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Matsubara
authors.forename: M
authors.initials: M
authors.lastname: Kanasaki
authors.forename: S
authors.initials: S
authors.lastname: Murasawa
authors.forename: Y
authors.initials: Y
authors.lastname: Tsukaguchi
authors.forename: Y
authors.initials: Y
authors.lastname: Nio
authors.forename: M
authors.initials: M
authors.lastname: Inada
mesh_terms: D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011945:Receptors, Angiotensin / Q000032:analysis / Q000235:genetics*
chemical_list: D011945:Receptors, Angiotensin; D000804:Angiotensin II; D003907:Dexamethasone