| First Author | Okoshi K | Year | 2004 |
| Journal | Circulation | Volume | 110 |
| Issue | 6 | Pages | 713-7 |
| PubMed ID | 15289373 | Mgi Jnum | J:130411 |
| Mgi Id | MGI:3771650 | Doi | 10.1161/01.CIR.0000138109.32748.80 |
| Citation | Okoshi K, et al. (2004) Neuregulins regulate cardiac parasympathetic activity: muscarinic modulation of beta-adrenergic activity in myocytes from mice with neuregulin-1 gene deletion. Circulation 110(6):713-7 |
| abstractText | 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. METHODS AND 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. |
