title: Enhanced inhibition of L-type Ca2+ current by beta3-adrenergic stimulation in failing rat heart.
abstract: beta3-adrenergic receptors (AR) have recently been identified in mammalian hearts and shown to be up-regulated in heart failure (HF). beta3-AR stimulation reduces inotropic response associated with an inhibition of L-type Ca2+ channels in normal hearts; however, the effects of beta3-AR activation on Ca2+ channel in HF remain unknown. We compared the effects of beta(3)-AR activation on L-type Ca2+ current (ICa,L) in isolated left ventricular myocytes obtained from normal and age-matched rats with isoproterenol (ISO)-induced HF (4 months after 340 mg/kg s.c. for 2 days). ICa,L was measured using whole-cell voltage clamp and perforated-patch recording techniques. In normal myocytes, superfusion of 4-[-[2-hydroxy-(3-chlorophenyl)ethylamino]propyl]phenoxyacetate (BRL-37,344; BRL), a beta3-AR agonist, caused a dose-dependent decrease in ICa,L with maximal inhibition (21%, 1.1 +/- 0.2 versus 1.4 +/- 0.1 nA) (p < 0.01) at 10(-7) M. In HF myocytes, the same concentration of BRL produced a proportionately greater inhibition (31%) in ICa,L (1.1 +/- 0.2 versus 1.6 +/- 0.2 nA) (p < 0.05). A similar inhibition of ICa,L was also observed with ISO (10(-7) M) in the presence of a beta1- and beta2-AR antagonist, nadolol (10(-5) M). Inhibition was abolished by the beta3-AR antagonist (S)-N-[4-[2-[[3-[3-(acetamidomethyl)phenoxy]-2-hydroxypropyl]amino]ethyl]phenyl]benzenesulfonamide (L-748,337; 10(-6) M), but not by nadolol. The inhibitory effect of BRL was attenuated by a nitric-oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (10(-4) M), and was prevented by the incubation of myocytes with pertussis toxin (PTX; 2 microg/ml, 36 degrees C, 6 h). In conclusion, beta3-AR activation inhibits L-type Ca2+ channel in both normal and HF myocytes. In HF, beta3-AR stimulation-induced inhibition of Ca2+ channel is enhanced. These effects are likely coupled with PTX-sensitive G-protein and partially mediated through a NOS-dependent pathway.
authors.affiliation: Cardiology Section, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157-1045, USA.
authors.forename: Zhu-Shan
authors.initials: ZS
authors.lastname: Zhang
authors.forename: Heng-Jie
authors.initials: HJ
authors.lastname: Cheng
authors.forename: Katsuya
authors.initials: K
authors.lastname: Onishi
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Ohte
authors.forename: Thomas
authors.initials: T
authors.lastname: Wannenburg
authors.forename: Che-Ping
authors.initials: CP
authors.lastname: Cheng
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000502:physiology; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006333:Heart Failure / Q000139:chemically induced / Q000503:physiopathology*; D006352:Heart Ventricles / Q000166:cytology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D032383:Myocytes, Cardiac / Q000187:drug effects; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D022702:Receptors, Adrenergic, beta-3 / Q000187:drug effects* / Q000502:physiology
chemical_list: D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D020746:Calcium Channels, L-Type; D022702:Receptors, Adrenergic, beta-3; D007545:Isoproterenol