Activation and inactivation of the osteoclast Ca²⁺ receptor by the trivalent cation, La³⁺

We report changes in the cytosolic Ca²⁺ concentration ([Ca²⁺]_i) of single rat osteoclasts in response to Ca²⁺ receptor activation by micromolar concentrations of the lanthanide metal cation, La³⁺. The extracellular application of La³⁺ induced a concentration-dependent elevation of cytosolic [Ca²⁺]. Prior conditioning of osteoclasts with La³⁺ resulted in a concentration-dependent reduction of the response to a subsequent application of a maximally effective concentration of Ni²⁺, a known agonist of the osteoclast Ca²⁺ receptor. The results establish that the osteoclast Ca²⁺ receptor is highly sensitive to activation and inactivation by the trivalent cation, La³⁺.