Nitric oxide formation caused by Ca2+ release from internal stores in neuronal cell line is enhanced by cyclic AMP

The influence of an elevated level of cyclic AMP on the formation of nitric oxide was investigated in a neuronal cell line (108CC15; NG108-15), in which we had previously shown that nitric oxide mediates the activation of soluble guanylyl cyclase upon stimulation with the hormones bradykinin, endothelin, and serotonin. Maximal amplitude and duration of cyclic GMP response to bradykinin were about 2-fold greater in cells with cyclic AMP levels increased by forskolin pretreatment than in control cells with basal levels of cyclic AMP. Phosphodiesterase inhibitors (isobutylmethylxanthine or M&B 22,948 (zaprinast)) similarly increased the maximal amplitude of the cyclic GMP response to bradykinin, but, in contrast, slowed down the decay phase of the cyclic GMP response to a much greater extent. The cyclic GMP responses to bradykinin were suppressed with the same potency by L-arginine analogues in control and in forskolin-treated cells (IC50 of NG-monomethyl-L-arginine 2 microM, of nitro-L-arginine 0.7 microM). The transient rises of cyclic GMP levels induced by bradykinin and endothelin, which both cause release of Ca2+ from internal stores, were similarly enhanced by forskolin pretreatment. However, the transient cyclic GMP response to serotonin which is due to Ca2+ influx into the neuronal cell line via 5-hydroxytryptamine3 (5-HT3) receptors was not affected by raising the cyclic AMP levels by forskolin pretreatment. Thus, cyclic AMP seems to enhance nitric oxide formation which depends on Ca2+ release from internal stores.