Figure 1.

Effects of extracellular Ca²⁺, l-Phe, and l-Trp on Ca²⁺ mobilization in HEK-293 cells stably expressing the human CaR. HEK-5001 cells growing on glass coverslips were loaded with fura-2 and exposed to test agents in a stirred fluorescence cuvette at 37°C in the light path of a fluorometer. In all three panels, baseline Ca²⁺_o was 0.5 mM, and 1-mM increments of Ca²⁺_o were applied at the open arrows. The vertical bars indicate the fluorescence ratios (340/380). (a) Lack of effect of 3 mM l-Phe (closed arrow) at basal (subthreshold) Ca²⁺_o (0.5 mM) and effect of repetitive 1-mM increments of Ca²⁺_o (open arrows). (b) Stereoselective mobilization of Ca²⁺ by 3 mM l-Phe but not 3 mM d-Phe (closed arrows) at 2.5 mM Ca²⁺_o. (c) Stereoselective mobilization of Ca²⁺ by 3 mM l-Trp but not 3 mM d-Trp (closed arrows) at 2.5 mM Ca²⁺_o.