Figure 8. NCC dephosphorylation shapes the BP response to dietary potassium.

(A) p-NCC (T38) or (B) t-NCC relative abundance versus plasma potassium relationships are shown for control mice (WT/WT SPAK, blue) and homozygous CA-SPAK mice (CA/CA, red) fed increasing amounts of potassium chloride (KCl) (circles) or potassium bicarbonate (KHOC₃) (squares) or a nominally potassium-free diet (triangles). p-NCC and t-NCC values were normalized to control mice on the control diet. Each data point represents a separate mouse. Lines through the p-NCC data are best fits to NCCp(max)/1+ IC₅₀/(K⁺)ⁿ, n = –2 IC₅₀ of WT/WT, 3.7, CA/CA 5.5 mM K⁺. Lines through the p-NCC data are fit to linear with a small but significant (P < 0.0001) non-zero slope. (C) Systolic BP (SBP), (D) diastolic BP (DBP), and (E) mean arterial pressure (MAP) versus plasma potassium relationships for control mice (blue) and CA-SPAK mice (red). Each data point represents the mean ± SEM of BP and plasma potassium levels from more than 5 mice after 4 days on each diet. Lines best fit to data are fit to BP(max)/1+ IC₅₀/(K⁺)ⁿ, with n fixed at 2 (IC₅₀ of WT/WT: SBP, 3.7 mM K⁺; DBP, 3.6 mM K⁺; MAP, 3.7 mM K⁺. IC₅₀ of CA/CA: SBP, 5.5 mM K⁺; DBP, 5.3 mM K⁺, MAP 5.3 mM K⁺). P values denote the significance of different fits for WT and CA SPAK mice. (F) SBP, (G) DBP, and (H) MAP versus relative p-NCC relationships. Data are derived from data shown in A–E. Each data point represents the mean ± SEM of BP. Lines best fit to 4 parameter logistic equations. P values denote the significance fit as the preferred model over the linear fit.