Nitric oxide inhibits ACh-induced intracellular calcium oscillations in porcine tracheal smooth muscle

With real-time confocal microscopy, the effect of three nitric oxide (NO) donors, S-nitroso-N-acetylpenicillamine, S-nitrosoglutathione, and diethylamine NO adduct, on the dynamic intracellular Ca²⁺ concentration ([Ca²⁺](i)) response of porcine tracheal smooth muscle (TSM) cells to acetylcholine (ACh) was examined. ACh initiated propagating [Ca²⁺](i) oscillations in TSM cells, which were inhibited by NO donors. 8- Bromoguanosine 3',5'-cyclic monophosphate slowed the frequency of [Ca²⁺](i) oscillations but did not completely inhibit oscillations, suggesting that the effects of NO donors are only partially mediated via guanosine 3',5'-cyclic monophosphate-dependent mechanisms. After preexposure to NO donors, ACh induced a small biphasic [Ca²⁺](i) response that was blocked by nifedipine, suggesting a lack of effect on Ca²⁺ influx through voltage-gated channels. In addition, NO donors did not inhibit Ca²⁺ influx induced by BAY K 8644. The [Ca²⁺](i) response to caffeine was inhibited by NO donors, indicating inhibition of sarcoplasmic reticulum (SR) Ca²⁺ release. When Ca²⁺ influx and SR Ca²⁺ reuptake were blocked, basal [Ca²⁺](i) increased, and this was inhibited by NO donors, suggesting enhanced Ca²⁺ efflux. These results indicate that NO donors inhibit [Ca²⁺](i) oscillations by blocking SR Ca²⁺ release and enhancing Ca²⁺ extrusion.