Figure 7. Sensitivity of various CaSR mutants to L-Phe in HEK293 cells.

a. HEK-293 cells transfected with CaSR or its mutants were loaded with Fura-2 AM for 15 min. The intracellular Ca²⁺ level was assessed by monitoring emission at 510 nm with excitation alternately at 340 or 380 nm using fluorescence microscopy as above. Each experiment started with 1.5 mM mM Ca²⁺ followed by stepwise increases in the level of L-Phe (up to 12.0 mM) while the [Ca²⁺]_o was maintained at 1.5 mM. b. The sensitivity of P221Q and L173P to L-Phe were compared at 5.0 mM [Ca²⁺]_o or 15.0 mM [Ca²⁺]_o, respectively.