Intercellular Communication: Renal, Urinary Bladder, Sensory, and Salivary Gland Cells.

In four epithelial cell systems (salivary gland, renal, urinary bladder, and sensory cells) cells are interconnected as far as much of their ion content is concerned. In the salivary gland and renal epithelia, all cells of the epithelium are interconnected; and communication between a given cell and any of its nearest neighbors is equally good. In the bladder and sensory epithelia, communication appears to be more restricted, manifesting itself in chains of connected cells in the former, and in small groups of connected cells in the latter. The permeability of the cell membrane at the junction between connected cells is several orders of magnitude greater than it is at the cell surface bordering the exterior of the cells. Each connected cell ensemble functions as a system with a fairly continuous cytoplasmic core bounded by a diffusion barrier which is continuous along the entire outer surface of the system. As a result, ions move rather freely from cell to cell, but not from cell interior to exterior. Intercellular communication in at least three epithelia is associated with the presence of certain close-junctional membrane complexes.