Different roles of alpha1-adrenoceptor subtypes in mediating cardiomyocyte protein synthesis in neonatal rats.
1. Three different alpha1-adrenoceptor subtypes, designated alpha1A, alpha1B and alpha1D, have been cloned and identified pharmacologically in cardiomyocytes. In vitro studies have suggested that alpha1-adrenoceptors play an important role in facilitating cardiac hypertrophy. However, it remains controversial as to which subtype of alpha1-adrenoceptors is involved in this response. In the present study, we investigated the different role of each alpha1-adrenoceptor subtype in mediating cardiomyocyte protein synthesis, which is a most important characteristic of cardiac hypertrophy in cultured neonatal rat cardiomyocytes. 2. Cardiomyocyte hypertrophy was monitored by the following characteristic phenotypic changes: (i) an increase in protein synthesis; (ii) an increase in total protein content; and (iii) an increase in cardiomyocyte size. 3. The role of each alpha1-adrenoceptor subtype in mediating cardiomyocyte protein synthesis was investigated by the effect of specific alpha1-adrenoceptor subtype-selective antagonists on noradrenaline-induced [3H]-leucine incorporation. In addition, pKB values for alpha1-adrenoceptor subtype-selective antagonists were calculated and compared with the corresponding pKi values to further identify their effects. 4. Activation of alpha1-adrenoceptors by phenylephrine or noradrenaline in the presence of propranolol significantly increased [3H]-leucine incorporation, protein content and cell size. 5. Pre-incubating cardiomyocytes with 5-methyl-urapidil, RS 17053 or WB 4101 significantly inhibited noradrenaline-induced [3H]-leucine incorporation. However, there was no effect when cardiomyocytes were pre-incubated with BMY 7378. The correlation coefficients between pKB values for alpha1-adrenoceptor subtype-selective antagonists and pKi values obtained from cloned alpha1A-, alpha1B- or alpha1D-adrenoceptors were 0.92 (P <0.01), 0.66 (P >0.05) and 0.24 (P >0.05), respectively. 6. Our results suggest that the alpha1-adrenoceptor is dominantly responsible for adrenergic hypertrophy of cultured cardiomyocytes in neonatal rats. The efficiency in mediating cardiomyocyte protein synthesis is alpha1A > alpha1B >> alpha1D.
Zhang
Yongzhen
Y
Institute of Vascular Medicine, Peking University Third Hospital and Key Laboratory of Molecular Cardiovascular Sciences, Ministry of Education, Beijing, PR China. zhangy@bjmu.edu.cn
Yan
Jie
J
Chen
Kai
K
Song
Yao
Y
Lu
Zhizhen
Z
Chen
Mingzhe
M
Han
Chide
C
Zhang
Youyi
Y
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D049108:Cell Enlargement; D002478:Cells, Cultured; D004146:Dioxanes / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007930:Leucine / Q000378:metabolism; D009124:Muscle Proteins / Q000096:biosynthesis*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000378:metabolism*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D007211:Indoles; D009124:Muscle Proteins; D010879:Piperazines; C099495:RS 17053; D018340:Receptors, Adrenergic, alpha-1; C057446:5-methylurapidil; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D007930:Leucine; C053428:BMY 7378; D009638:Norepinephrine; D011224:Prazosin