Myocyte nitric oxide synthase 2 contributes to blunted beta-adrenergic response in failing human hearts by decreasing Ca2+ transients.
BACKGROUND
Human heart failure (HF) usually exhibits blunted response to beta-adrenergic receptor (AR) stimulation. Here, we examined whether expression of nitric oxide synthase-2 (NOS2, or inducible NOS) contributes to this loss of inotropic reserve in human HF.


RESULTS
Failing human hearts were obtained at transplantation. Contraction and [Ca2+]i measurements were performed in isolated cardiac myocytes and trabeculae. In HF myocytes and muscle, isoproterenol (ISO), a beta-AR agonist, led to small inotropic and lusitropic responses. Specific inhibition of NOS2 by aminoguanidine (AG) or L-NIL dramatically increased the ISO-induced inotropy and lusitropy, such that the ISO+AG response in HF approached that seen with ISO alone in nonfailing human myocytes or muscles. Ca2+ transient data directly paralleled these results, indicating that altered cellular Ca2+ handling is responsible. In nonfailing human hearts, NOS2 inhibition had no effects. In addition, NOS2 inhibition also had no effect in 30% of failing hearts, but in these myocytes and muscles, the ISO response alone was similar to that of nonfailing hearts. In line with these functional findings, NOS2 protein expression measured by Western blotting was induced in HF when AG/L-NIL had a functional effect but not when AG/L-NIL had no effect on contractility and Ca2+ transients.


CONCLUSIONS
NOS2 expression strongly limited ISO-induced increases in contraction, twitch Delta[Ca2+]i, and lusitropy in trabeculae and isolated myocytes from failing human hearts. Thus, the beta-AR hyporesponsiveness in human HF is mediated in large part by NO (or related congeners) produced within cardiac myocytes via NOS2.
Ziolo
Mark T
MT
Department of Physiology, Loyola University Medical Center, Maywood, Ill 60153, USA.
Maier
Lars S
LS
Piacentino
Valentino
V
Bossuyt
Julie
J
Houser
Steven R
SR
Bers
Donald M
DM
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002303:Cardiac Output, Low / Q000201:enzymology* / Q000378:metabolism / Q000503:physiopathology*; D002478:Cells, Cultured; D046508:Culture Techniques; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006321:Heart / Q000187:drug effects / Q000503:physiopathology; D006352:Heart Ventricles / Q000166:cytology; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000201:enzymology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D000318:Adrenergic beta-Agonists; D004791:Enzyme Inhibitors; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D007545:Isoproterenol; D002118:Calcium