TABLE 3

Potency and maximal effect of extracellular Ca²⁺ and R-568 to the wild-type and various mutant hCaSRs in Ca²⁺ flux and IP assays

Potency and maximal effect of extracellular Ca²⁺was compared in the absence and presence of R-568. Parameter values were obtained by nonlinear regression analysis using the variable slope Hill equation as described under Materials and Methods. Values represent the mean ± S.D. of 3 to 4 experiments.

	0 μM R-568		33 μM R-568		EC1₅₀/EC2₅₀^{^b}	E2/E1^{^c}
	Log EC₅₀	E_max	Log EC₅₀	E_max	EC1₅₀/EC2₅₀^{^b}	E2/E1^{^c}
Aequorin Assay
Mutant
F809L	−2.05 ± 0.07	137 ± 15	−2.90 ± 0.03^**	195 ± 21^*	7.0	1.4
R185Q	>−1.2	27 ± 10^{^a}	−2.06 ± 0.04	251 ± 107	>6.9	9.4
F180C	>−1.2	38 ± 4^{^a}	−2.12 ± 0.05	261 ± 39	>7.9	6.9
Y218C	>−1.2	14 ± 6^{^a}	−1.92 ± 0.06	150 ± 21	>5.0	10.5
P39A	−1.85 ± 0.08	129 ± 20	−2.54 ± 0.07^**	187 ± 53	5.0	1.5
L13P	−1.95 ± 0.06	46 ± 22	−2.50 ± 0.09^**	75.3 ± 26	3.6	1.6
Inositol Phosphate Accumulation Assay
Mutant
F809L	−2.05 ± 0.02	11.3 ± 0.6	−2.79 ± 0.02^**	27.7 ± 2.1^**	5.6	2.4
R185Q	−1.52 ± 0.08	25.7 ± 1.5	−2.17 ± 0.07^**	46.7 ± 3.5^**	4.5	1.8
F180C	−1.68 ± 0.02	14.3 ± 2.1	−2.32 ± 0.05^**	39.0 ± 2.7^**	4.4	2.7
Y218C	−1.53 ± 0.13	4.6 ± 2.9	−1.89 ± 0.10^*	15.0 ± 3.5^*	2.3	3.3
P39A	−2.02 ± 0.01	10.2 ± 3.3	−2.60 ± 0.23^*	12.7 ± 3.8	3.8	1.2
L13P	−1.89 ± 0.27	4.1 ± 0.8	−2.22 ± 0.30	5.0 ± 0.5	2.2	1.2

↵* Significantly different from Log EC₅₀ in the absence of R-568. P < 0.05 (ttest).
↵** Significantly different from Log EC₅₀ in the absence of R-568. P < 0.001 (ttest).
↵^a Response at the highest concentration of extracellular Ca²⁺ tested (60 mM).
↵^b Ratio of the EC₅₀ in the absence of R-568 to the EC₅₀ in the presence of 33 μM R-568.
↵^c Ratio of maximal response in the presence of 33 μM R-568 to the maximal response in the absence of R-568.