Neuregulins regulate cardiac parasympathetic activity: muscarinic modulation of beta-adrenergic activity in myocytes from mice with neuregulin-1 gene deletion.
BACKGROUND
Neuregulins are required for maintenance of acetylcholine receptor-inducing activity of nicotinic receptors in neurons and skeletal muscle, but effects of neuregulins on muscarinic receptors are not known. In the normal heart, parasympathetic activation counterbalances beta-adrenergic activation. To test the hypothesis that neuregulins modify parasympathetic function in the heart, we studied cardiomyocytes from mice heterozygous for neuregulin-1 gene deletion (NRG-1+/-) and examined the effects of beta-adrenergic stimulation on contractility in the presence and absence of the muscarinic agonist carbachol.


RESULTS
We evaluated contraction and intracellular Ca2+ transients ([Ca2+]i) in left ventricular (LV) myocytes loaded with Fluo-3 from NRG-1+/- and wild-type (WT) mice. Under baseline conditions (0.5 Hz, 1.5 mmol/L [Ca2+]o, 25 degrees C), characteristics of myocyte contraction/relengthening and systolic/diastolic [Ca2+]i were not different between WT and NRG-1+/- mice. The steady-state increases in fractional shortening (FS) and peak-systolic [Ca2+]i in response to isoproterenol were similar in both groups. In WT myocytes stimulated with isoproterenol, carbachol decreased FS, peak-systolic [Ca2+]i, and cAMP levels. In NRG-1+/- myocytes, carbachol did not attenuate either FS or peak-systolic [Ca2+]i, associated with the failure to decrease cAMP levels. Investigation of muscarinic receptor signaling showed no difference of LV protein levels of muscarinic M2 receptors or G protein Galpha(i1,2), Galpha(i3), and Galpha(o) subunits.


CONCLUSIONS
Cardiomyocytes deficient in neuregulin signaling are unable to adequately counterbalance beta-adrenergic activation by inhibitory parasympathetic activity. This mechanism may contribute to the known increased risk of heart failure in injured human hearts when neuregulin signaling is suppressed.
Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Mass 02215, USA.
Katashi
K
Okoshi
Masaharu
M
Nakayama
Xinhua
X
Yan
Marina P
MP
Okoshi
Adam J T
AJ
Schuldt
Mark A
MA
Marchionni
Beverly H
BH
Lorell
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured / Q000187:drug effects / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology; D017353:Gene Deletion; D006329:Heart Conduction System / Q000187:drug effects / Q000502:physiology; D006579:Heterozygote; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D018721:Muscarinic Agonists / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology; D020890:Neuregulin-1 / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D043585:Receptor, Muscarinic M2 / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology
D000318:Adrenergic beta-Agonists; C495964:Chrnb1 protein, mouse; D018721:Muscarinic Agonists; D020890:Neuregulin-1; D043585:Receptor, Muscarinic M2; D011978:Receptors, Nicotinic; D002217:Carbachol; D000242:Cyclic AMP; D007545:Isoproterenol