Autonomic Nervous System and Epithelia: Integration and Control

Adenosine triphosphate (ATP) has emerged as a signaling molecule released during mechanical stimulation in a variety of cells including urinary bladder, human colon, and nasal epithelium (Chien et al., 1998; Cooke et al., 2003; Wynn et al., 2004). One of the pathways for 5-HT release is mechanosensitive and involves early release of ATP (Fig. 1C). Rotational shaking of BON cells (60–100 rpm), and mucosal stroking of the intestinal lining with a brush can stimulate enterochromaffin cells and can thus be converted to a biological event such as opening of a mechanosensitive ion channel (Kim et al., 2001a). ATP then exits the sensory enterochromaffin cell by unknown mechanisms that could include exocytosis of secretory granules or efflux through ion channels (Wynn et al., 2004). Once ATP leaves the cell and reaches the extracellular compartment, it can act as an autocrine messenger to stimulate other endochromaffin cells directly or as a paracrine messenger to activate P2Y receptors or P2X receptors that may be present on intrinsic afferent neurons (Figs. 1B, C, 2).