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

Abstract

Altered expression and functional responses to cardiac β3-adrenergic receptors (ARs) may contribute to progressive cardiac dysfunction in heart failure (CHF). We compared myocyte β3-AR mRNA and protein levels and myocyte contractile, [Ca2+] i transient, and Ca2+ current (ICa.L) responses to BRL-37344 (BRL, 10-8 mol/L), a selective β3-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 β3-AR mRNA from myocyte total RNA in each animal. Using a cloned canine β3-AR cDNA probe and myocyte poly A+ RNA, we detected a single band about 3.4 kb in normal and CHF myocytes. β3-AR protein was detected by Western blot. β3-AR mRNA and protein levels were significantly greater in CHF myocytes than in normal myocytes, Importantly, these changes were associated with enhanced β3-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 ICa.L. These responses were not modified by pretreating myocytes with metoprolol (a β1-AR antagonist) or nadolol (a β1- and β2-AR antagonist), but were nearly prevented by bupranolol or L-748,337 (β3-AR antagonists). We conclude that in dogs with pacing-induced CHF, β3-AR gene expression and protein levels are upregulated, and the functional response to β3-AR stimulation is increased. This may contribute to progression of cardiac dysfunction in CHF.