Figure 3.

cAMP-induced inhibition of NHE3. Stably transfected PS120 fibroblasts acidified with NH₄Cl were either recovered in Na⁺ medium (○) or treated with 0.5 mM 8-Br-cAMP for 5–10 min before the recovery in Na⁺ medium (▴). Na⁺/H⁺ efflux rates were calculated at various pH_i, and lines were fitted to the data using an allosteric model. Treatment of (A) PS120/NHE3V/NHERF with 0.5 mM 8-Br-cAMP (▴) inhibited the Na⁺/H⁺ exchange activity with a decrease in V_max by ≈30% with no effect on K′(H_i⁺) or n_app. (C) Similarly, PS120/NHE3V/GST-E3KARP was inhibited by 8-Br-cAMP by a decrease in V_max by ≈28%. In contrast, PS120/NHE3 (B) and PS120/NHE3/GST (D) were not affected by 8-Br-cAMP. Shown here are data from four or more experiments for each condition.