Calcium‐activated calcium permeability in parathyroid cells

Abstract

The Ca²⁺ receptor mechanism of the parathyroid cell was studied using La³⁺ as a probe. La³⁺ was found to bind to the cell surface without further penetration. Measurements of ⁴⁵Ca fluxes and the cytoplasmic Ca²⁺ concentration (Ca_i ²⁺) revealed a stimulatory component in the action of La³⁺ on Ca²⁺ permeability resulting in a rise in Ca_i ²⁺ These effects mimicked those obtained when raising the extracellular Ca²⁺ concentration from 0.5 to 3.0 mM, but the actions of La³⁺ and Ca²⁺ were not additive. The results suggest the existence of a novel Ca²⁺ permeability physiologically activated by binding of Ca²⁺ to an external receptor.