Fig. 2

Pi inhibits the CaSR in a noncompetitive manner. a Representative immunoblot showing Pi-mediated inhibition of CaSR-induced pERK after 10 min of treatment with Pi and acidosis (pH 7.2). Changes in pERK were determined by densitometry, corrected for β-actin abundance and normalized to Pi-free CaSR-stimulated control (n = 8 dishes from four experiments; 0.5 mM Ca²⁺ shown as a negative control). b Representative traces showing \({\mathrm{Ca}}_i^{2 + }\) mobilization from single cells exposed to buffers containing increasing levels of \({\mathrm{Ca}}_o^{2 + }\) (left), and Ca²⁺ concentration-effect curves (right) in the presence of 0 (n = 7), 0.8 (n = 9), and 2 (n = 10) mM Pi from three independent experiments. E_max expressed as %mean ± SEM. c Pi concentration-effect curves for \({\mathrm{Ca}}_i^{2 + }\)-mobilization upon stimulation with cinacalcet and 1 or 1.5 mM \({\mathrm{Ca}}_o^{2 + }\) (n = 7, two independent experiments). d SO₄ concentration-effect curves for \({\mathrm{Ca}}_i^{2 + }\)-mobilization upon stimulation with R568 and 1.5 mM \({\mathrm{Ca}}_o^{2 + }\) (n = 8, two independent experiments). b–d Area under the curve was calculated for each treatment and normalized to maximal response. Data were fitted to a four-parameter Hill equation (Eq. (1)) for sigmoidal dose response variable slope, and fitted best when EC₅₀ (b)/IC₅₀ (c, d), expressed as mean (95% confidence interval), were shared among data sets, P < 0.01 extra sum-of-square F-test. Data expressed as %mean ± SEM. Data were analyzed by using RM-ANOVA with Dunnett’s multiple comparisons, ns not significant; *P < 0.05, **P < 0.01, and ***P < 0.001. Source data are provided as a Source Data file