Methylene Blue acts as a GCS (guanylyl cyclase) inhibitor, biological stain and redox indicator. Methylene Blue inhibits tau filament formation. Additionally, Methylene Blue is also reported to inhibit NOSs (nitric oxide synthase). Methylene Blue is widely used to inhibit cGMP-mediated processes. Methylene Blue has been observed to dose-dependently induce cytotoxicity in U-373 MG human astrocytoma and SK-N-MC human neuroblastoma cells. Furthermore Methylene Blue is reported to bind to the M2 subtype of muscarinic receptors in rat cardiac myocytes, and thus exhibit antimuscarinic effects on IK, ACh and ICa. Methylene Blue has also been reported to inhibit endothelium-dependent relaxation of isolated blood vessels.An inhibitor of cGMP-mediated processes and guanylyl cyclase, a useful stain, and a redox indicator