Diagram representing acinar salivary secretion and TJ proteins. Activation of basolateral M3 muscarinic receptors by neurotransmitters (e.g., acetylcholine) initiates signaling cascades that stimulate apical Ca2+-dependent Cl channels. The stimulated efflux of Cl produces a transepithelial potential difference that drives Na+ and H2O transport across the TJ. Alternatively, H2O can reach the lumen by water channels. These events create a plasma-like primary secretion in the lumen. As the primary saliva passes through the ducts, Na+ and Cl are reabsorbed and K+ is secreted into the lumen. Inset (adapted from [55]) indicates the TJ proteins occludin, claudin, and JAM linked to the cytoskeleton via cytoplasmic ZO proteins. Clearly TJ structure varies depending on the cell function; the question is how combinations of TJ proteins define function in acinar and ductal cells.
