Neuregulin-1{beta}1 rapidly modulates nitric oxide synthesis and calcium handling in rat cardiomyocytes.

Aims The ErbB-neuregulin1beta1 (Nrg1beta1) pathway is required for cardiac development and exerts chronic effects on the postnatal adult heart. Long term application results in hypertrophy and protection against oxidative stress and cytotoxic agents. We performed experiments with Nrg1beta1 acute treatment to find evidence for a further protective role due to rapid modulation of adult cardiomyocytes function. Methods and Results in confocal fluorimetric measurements Nrg1beta1 induced a calcium independent increase in nitric oxide (NO) production in isolated adult rat ventricular myocytes (ARVCMs), blocked by the phosphoinositide-3-kinase (PI3K) inhibitor Wortmannin (Wm). Western blot analysis showed enhancement in endothelial Nitric Oxide Synthase (eNOS) phosphorylation in Nrg1beta1 treated ARVCMs, attenuated by Wm. Nrg1beta1 induced a significant increase in calcium transient amplitude (indo-1 ratiometric measure) and accelerated the recovery of cytosolic calcium in the sarcoplasmic reticulum (SR) without affecting whole cell L-Type calcium current. Wm or the Protein Kinase-G (PKG) inhibiting peptide (DT-2) abolished the increase in calcium transient amplitude and the acceleration of calcium recovery induced by Nrg1beta1 treatment. Immunofluorescence analysis revealed that Nrg1beta1 treatment increased phospholamban phosphorylation and the effect was blocked by PI3K and PKG inhibition. Caffeine releasable SR calcium content was also higher during Nrg1beta1 administration. Conclusion Rapid activation of PI3K, eNOS and PKG and a consequent improvement in diastolic calcium can therefore be added to established Nrg1 protective roles.