Nitric oxide-sensitive guanylyl cyclase (NO-GC) is activated by the signaling molecule NO and produces cGMP. In the gastrointestinal (GI) tract nitrergic neurons release NO as neurotransmitter and are part of the enteric nervous system which regulates GI motility. In addition to smooth muscle cells (SMC), interstitial cells of Cajal (ICC) are implicated in nitrergic relaxation. In this study, we attended to clarify the role of GI NO-GC regarding nitrergic relaxation in mice.

We generated mouse lines that lack NO-GC ubiquitously (total GCKO), specifically in SMC (SM-GCKO) or in ICC (ICC-GCKO) and in both SMC and ICC (dbl-GCKO). Isometric force studies were performed to investigate the effects of NO on murine fundus. Immunohistochemistry was conducted to evaluate the expression of NO-GC in the different GI cell types.

NO-dependent relaxation of fundus smooth muscle was abolished in total GCKO mice. In SM-GCKO, NO still led to partial relaxation whereas ICC-KO showed a WT-like phenotype. Only in dbl-GCKO we observed lack of nitrergic relaxation similar to that seen in total GCKO mice. Immunohistochemistry revealed NO-GC expression in SMC, ICC and, surprisingly, in a third cell type characterized as fibroblast-like cells (FLC).

In conclusion, nitrergic GI relaxation is not evoked exclusively via NO-GC in SMC. Lack of NO-GC in both SMC and ICC, though, abolishes nitrergic signaling. In the fundus of dbl-GCKO mice strong NO-GC expression was still detected in FLC. By measuring resting membrane potential and inhibitory junction potentials we will further investigate the communication between these three different cell types.