Nrg-1 modulation of contractility and NO synthesis in isolated ventricular myocytes

Neuregulins (Nrg) are a family of growth factors that mediate cellular interactions through the activation of tyrosine kinase receptors of the ErbB family. The ErbB-Nrg pathway is a critical mediator of cardiac development and in the adult heart is involved in different process, including regulation of survival, hypertrophic growth, proliferation and modulation of contractility. We investigated the effects induced by the recombinant binding domain of Nrg1? 1 on calcium current (ICa), intracellular calcium, NO synthesis and NOS modulation in isolated adult rat ventricular myocytes. We assessed the presence of Nrg1 receptor ErbB4 and its preferential dimerization companion ErbB2 by immunofluorescence staining. Simultaneous measurements of intracellular calcium and nitric oxide with fluorescent probes on isolated cardiomyocytes showed that Nrg1? 1 induces a calcium independent increase in NO production, blocked by the PI3K inhibithor Wortmannin. Immunofluorescence and Western blot experiments evidenced that Nrg1? 1 stimulates eNOS phosphorylation (ser1179). Moreover, Nrg1? 1 enhanced basal calcium transients amplitude on field stimulated cells, but not basal or Iso-stimulated ICa in patch-clamp experiments. In conclusion, in isolated ventricular myocytes, Nrg1? 1 increases eNOS phosphorylation, NO production and calcium transients amplitude, without affecting basal calcium and ICa. Further investigations will be done to elucidate the mechanisms (direct or cGMP mediated) involved in the calcium transients amplitude enhancement.