Extracellular cation sensing by the enterocyte: Prediction of a novel divalent cation "receptor"

We report that the divalent cation Ni²⁺ elicits elevations in the cytosolic free Ca²⁺ concentration ([Ca²⁺]) in cultured enterocytes. These elevations were monophasic, each response consisting of a rapid initial transient rise of cytosolic [Ca²⁺] to a peak value followed by an exponential decline. The magnitude of the cytosolic [Ca²⁺] elevation varied with the concentration of applied Ni²⁺. In some cells, a single application of Ni²⁺ induced oscillatory changes in cytosolic [Ca²⁺]. There was also evidence for use-dependent inactivation: a conditioning application of Ni²⁺ substantially attenuated the response resulting from its subsequent application. Our findings thus demonstrate the existence of a divalent cation-sensing "receptor" on the enterocyte. This putative receptor may play a role in regulating mineral absorption across the enterocyte membrane.