Figure 1.

Schematic representation of intercellular communication mediated by the calcium-sensing Receptor (CaR) in polarized epithelial cells. When a Ca²⁺-mediated agonist (red circle) binds a specific receptor, Ca²⁺ concentration (yellow line) increases within the cytosol. Extrusion of Ca²⁺ via the plasma membrane Ca²⁺-ATPase (PMCA), localized at the apical membrane, might activate the CaR expressed on cells in close proximity (paracrine message) or on the same cell (autocrine message). The asymmetrical changes in extracellular Ca²⁺ are the result of the polarized localization of PMCA and store-operated channels (SOCs) at the apical and basolateral membranes, respectively. These fluctuations can be recorded with Ca²⁺-sensitive microelectrodes. Modified from [29].