Calcium-dependent release of NO from intracellular S-nitrosothiols

The paper describes a novel cellular mechanism for rapid calcium‐dependent nitric oxide (NO) release. This release occurs due to NO liberation from S ‐nitrosothiols. We have analysed the changes of NO concentration in acutely isolated pancreatic acinar cells. Supramaximal acetylcholine (ACh) stimulation induced a Ca 2+ ‐dependent increase in the fluorescence in the majority of cells loaded with the NO probe DAF‐FM via a patch pipette. The ACh‐induced NO signals were insensitive to inhibitors of calmodulin and protein kinase C but were inhibited by calpain antagonists. The initial part of the NO signals induced by 10 μM ACh showed little sensitivity to inhibition of NO synthase (NOS); however, cell pretreatment with NO donors (increasing cellular S ‐nitrosothiol contents) substantially enhanced the initial component of NO responses. Pancreatic acinar cells were able to generate fast calcium‐dependent NO responses when stimulated with physiological or supramaximal doses of secretagogues. Importantly, the source of this NO is the already available S ‐nitrosothiol store rather than de novo synthesis by NOS. A similar mechanism of NO release was found in dorsal root ganglia neurons.