Fig. 6.

Na⁺ transport in IMCD3 cells is primarily mediated by ENaC. A: representative calibration recordings of 28 simultaneously monitored cells. Cells loaded with SBFI were superfused with Na-HEPES physiological saline as detailed in materials and methods (rest) and then with calibration solution containing ionophores (5 μm nigericin+5 μM monensin) to permeabilize the cell membrane and equilibrate the intracellular environment [intracellular Na⁺ concentration ([Na⁺]_i)] with the external solution over a range of 0 to 140 mM as indicated above the trace. B. plots of [Na⁺]_i vs. 340/380 ratio. Data points from 3 experiments of the type shown in A were fitted using nonlinear least squares regression as described (36). C. representative tracings in the absence or presence of ENaC-specific inhibitor benzamil (Ben). The procedure was as in A except that the cells were superfused with Na-HEPES physiological saline with addition and removal of benzamil (1 μM) as indicated. D: [Na⁺]_i from 3 independent experiments (n = 3) of the type shown. The calibration curve shown in B was used to calculate [Na⁺]_i. *P < 0.05 vs. −Ben (before addition of the inhibitor).