Induction of beta_3-Adrenergic Receptor Functional Expression following Chronic Stimulation with Noradrenaline in Neonatal Rat Cardiomyocytes

摘要

This study aimed to characterize beta_3-adrenergic receptors(ARs)in rat neonatal cardiomyocytes using the noradrenaline(NOR)properties to modulate the expression and function of the three beta-ARs.We assessed the effect of NOR(physiological nonse-lective agonist),isoprenaline(ISO,beta-nonselective agonist),do-butamine(DOB,beta_1-selective agonist),and procaterol(PROC,beta_2-selective agonist)on cAMP accumulation using cardiomyocytes untreated or treated with 100 muM NOR for 24 h.The inhibition of forskolin-stimulated cAMP accumulation was determined using NOR,isoprenaline,and the beta_3-selective agonists 4-[2-[(2-(3-chlorophenyl)-2-hydroxyethyl)amino]pro-pyl]phenoxyacetic acid(BRL 37344)and 5-[-2-([-2-(3-chlorophenyl)-2-hydroxyethyl]amino)propyl]-1,3-benzodioxole-2,2-dicarboxylate(CL 316243).The experiments were performed in the absence or presence of propranolol or 2-hy-droxy-5-[2-[[2-hydroxy-3-[4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]phenoxy]propyl]amino]ethoxy]-benzamide meth-anesulfonate(CGP 20712A)and/or 1-[2,3-(dihydro-7-meth-yl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hy-drochloride(ICI 118551)to inhibit beta_1-and beta_2-AR stimulation and 1-(2-ethylphenoxy)-3-[[1S)-1,2,3,4-tetrahydro-1-naphtha-lenyl]amino-(2S)-2-propanol hydrochloride(SR 59230A)(beta_3-selective antagonist).In addition,the level of the three subtypes was determined by reverse transcription polymerase chain reaction and Western blotting.NOR pretreatment decreased the activation of cAMP induced by NOR,isoprenaline,and DOB,whereas PROC response was abolished.The inhibition of NOR response by CGP 20712A or ICI118551 demonstrated that beta_1-and beta_2-ARs are down-regulated and that beta_2-AR functional activity was also abolished in cardiomyocytes exposed to chronic stimulation.beta_3-AR function was observed with NOR and ISO when beta_1-/beta_2-ARs were blocked and with both beta_3-selective agonists in NOR-treated cells only.This response was completely inhibited by SR 59230A and involved G_i protein.Furthermore,the results from functional studies agree well with those from expression experiments.In conclusion,these data provide strong evidence that beta_3-ARs are functionally up-regulated and coupled to G_i protein in rat neonatal cardiomyocytes following chronic exposure to NOR when beta_1-and beta_2-ARs are down-regulated.