Nitric oxide modulates signaling between cultured adult peripheral cardiac neurons and cardiomyocytes

To determine whether nitric oxide (NO) modifies cardiomyocytes directly or indirectly via peripheral autonomic neurons, the effects of NO were studied in long-term (3-6 wk) cultures of adult guinea pig ventricular myocytes alone as well as in cocultures with adult extracardiac (stellate ganglion) or intrinsic cardiac neurons. NADPH diaphorase was associated histochemically with cultured intrinsic cardiac and, to a lesser extent, stellate ganglion neurons. The beating frequency of ventricular myocytes cocultured with intrinsic cardiac neurons (M-intrinsic) or stellate ganglion neurons (M- stellate) increased by 20-30% (P < 0.001) after administration of the NO donor S-nitroso-N-acetylpenicillamine (SNAP); this effect was abolished by the guanylate cyclase inhibitor LY-83583. The beating frequency of noninnervated myocyte cultures was not affected by SNAP. The precursor of NO, L-arginine, also increased the beating rate (~20%; P < 0.05) of M-intrinsic cocultures, not affecting that of M-stellate cocultures or noninnervated myocyte cultures. Augmentor effects induced by SNAP were no longer elicited in the presence of tetrodotoxin and were unaffected by β-adrenergic or muscarinic receptor blockade. It is concluded that 1) NO-sensitive neurons are present in stellate and intrinsic cardiac ganglia, and these neurons increase the beating rate of cardiomyocytes in the presence of NO; 2) more NO-synthesizing neurons are present in M-intrinsic than M-stellate cocultures, since L-arginine increased the beating frequency of myocytes significantly only in M-intrinsic cocultures; and 3) the beating rate of noninnervated myocyte cultures is not directly affected by NO.