Figure 8.

Bile acids regulate ENaC in mpkCCD_c14 cells. Polarized mpkCCD_c14 cells grown on permeable supports were mounted in an Ussing chamber for I_SC measurements. A, representative recordings shown. Increasing concentrations of t-CA or t-HDCA were added to Ringer's buffer supplemented with 10 μm camostat on the apical side of the chamber, as indicated. After the last bile acid addition, bile acids were removed by replacing the solution on the apical side with Ringer's buffer lacking camostat. 2 μm trypsin was then added, followed by 10 μm amiloride. Baseline amiloride-sensitive I_SC was 16 ± 9 μA/cm². B, changes in current in response to t-CA (n = 6) or t-HDCA (n = 6) were determined as a percentage of the amiloride-sensitive baseline current, while correcting for time-dependent changes in current. Linear estimates of the time-dependent change in current under each condition were determined using a 30-s window during the steady-state period just before each bile acid addition and were used to account for run-down during each experiment. A dose–response experiment for t-CA activation of ENaC-expressing oocytes is overlaid for comparison (n = 5) and was performed analogously to the experiment in Fig. 1C. Data for t-CA were fit to the Hill equation, EC₅₀ = 210 ± 100 μm in mpkCCD_c14 cells and 148 ± 5 μm in oocytes.