OCLN and Parkinson disease: Of note, M3R is known as an activator of cytoplasmatic phospholipase A2 via the activation of protein kinase c (PKC) [75] and since PKC itself has been shown to play a role in the modulation of tight junction proteins such as occludin [65], it is possible, that M3 receptors may be involved in the modulation of epithelial barrier permeability both via modulation of tight junction proteins and transcellular permeability in patients with PD.