FIGURE 6.
Dose-response characteristics of ERK1/2 phosphorylation for the WT AT1R and the AT1R-Gq fusion over a broad range of AngII concentrations. Shown is the effect of the balanced agonist AngII on ERK1/2 phosphorylation in cells stably expressing WT AT1R and AT1R-Gq fusion protein under isotonic (288 mOsm/kg) or hypotonic osmotic stretch (191 and 143 mOsm/kg) conditions. A, representative immunoblots showing enhanced ERK1/2 phosphorylation in cells expressing the WT AT1R in response to increasing hypotonic osmotic stretch over a range of AngII concentrations. B, osmotic stretch enhances ERK1/2 phosphorylation by increasing Emax without a change in the EC50 for the WT AT1R over a broad range of AngII concentrations. Isotonic 288 mOsm/kg (Emax = 1.90 ± 0.12, LogEC50 = −10.01 ± 0.45 nm); hypotonic 191 mOsm/kg (Emax = 2.35 ± 0.10, LogEC50 = −10.88 ± 0.33 nm); hypotonic 143 mOsm/kg (Emax = 2.51 ± 0.08, LogEC50 = −11.29 ± 0.30 nm) (n = 5–6 independent experiment at each AngII concentration). Emax, p < 0.005, hypotonic 143 mOsm/kg versus isotonic 288 mOsm/kg; Emax, p < 0.05, 191 mOsm/kg versus isotonic 288 mOsm/kg (one-way ANOVA with Bonferroni correction). There was no significant difference for LogEC50 between groups. C, representative immunoblots in cells stably expressing AT1R-Gq fusion proteins showing no enhancement of ERK1/2 phosphorylation in response to increasing hypotonic osmotic stretch over a range of AngII concentrations in cells. D, osmotic stretch does not enhance ERK1/2 phosphorylation in cells stably expressing AT1R-Gq fusion proteins in response to AngII stimulation. Isotonic 288 mOsm/kg (Emax = 2.84 ± 0.16, LogEC50 = −10.45 ± 0.31 nm); hypotonic 191 mOsm/kg (Emax = 2.84 ± 0.17, LogEC50 = −10.51 ± 0.16 nm); hypotonic 143 mOsm/kg (Emax = 2.83 ± 0.12, LogEC50 = −10.68 ± 0.20 nm) (n = 5–6 independent experiment at each AngII concentration). There was no significant difference for both Emax and LogEC50 between groups.