Upregulation of functional β3-adrenergic receptor in the failing canine myocardium

Altered expression and functional responses to cardiac beta (3)-adrenergic receptors (ARs) may contribute to progressive cardiac dysfunction in heart failure (CHF). We compared myocyte beta (3)-AR mRNA and protein levels and myocyte contractile, [Ca2+](i) transient, and Ca2+ current (I-Ca.L) responses to BRL-37344 (BRL, 10(-8) mol/L), a selective beta (3)-AR agonist, in 9 instrumented dogs before and after pacing-induced CHF. Myocytes were isolated from left ventricular myocardium biopsy tissues. Using reverse transcription-polymerase chain reaction, we detected beta (3)-AR mRNA from myocyte total RNA in each animal. Using a cloned canine beta (3)-AR cDNA probe and myocyte poly A(+) RNA, we detected a single band about 3.4 kb in normal and CHF myocytes. beta (3)-AR protein was detected by Western blot. beta (3)-AR mRNA and protein levels were significantly greater in CHF myocytes than in normal myocytes. Importantly, these changes were associated with enhanced beta (3)-AR-mediated negative modulation on myocyte contractile response and [Ca2+](i) regulation. Compared with normal myocytes, CHF myocytes had much greater decreases in the velocity of shortening and relengthening with BRL accompanied by larger reductions in the peak systolic [Ca2+](i) transient and I-Ca.L. These responses were not modified by pretreating myocytes with metoprolol (a beta (1)-AR antagonist) or nadolol (a beta (1)- and beta (2)-AR antagonist), but were nearly prevented by bupranolol or L-748,337 (beta (3)-AR antagonists). We conclude that in dogs with pacing-induced CHF, beta (3)-AR gene expression and protein levels are upregulated, and the functional response to beta (3)-AR stimulation is increased. This may contribute to progression of cardiac dysfunction in CHF.