Figure 4.
NHE3 basal transport activity is reduced by both internal Class II PBM mutants NHE3CLDM/EK (or NHE3 PBMIImut) and C-terminal NHE3 Δ4. A, basal transport activity of NHE3 is decreased in internal Class II PBM mutants NHE3CLDM/EK (or NHE3 PBMIImut) and NHE3CLDM/QA but not in the putative internal Class I PBM mutant NHE3SAV/AA. Basal NHE3 activity was determined using BCECF as described under “Experimental Procedures.” Shown are the results of a single experiment, which was repeated at least four times with Vmax mean ± S.D. shown in the inset. Error bars represent S.D. p values compare the basal activities of NHE3 PBMIImut and NHE3CLDM/QA with NHE3 WT (unpaired t test). B, basal transport activity of NHE3 (Vmax) was decreased in both internal Class II PBM mutation NHE3 PBMIImut and C-terminal Class I PBM mutation NHE3 Δ4 and was further decreased in the combination NHE3 PBMIImut + Δ4. Shown are the results of a single experiment, which was repeated at least five times with Vmax mean ± S.D. shown in the inset. Error bars represent S.D. p values compare the basal activities of NHE3 PBMIImut and NHE3 Δ4 with NHE3 WT and of NHE3 PBMIImut + Δ4 with NHE3 Δ4 (unpaired t test). NS, not significant.