FIGURE 3.
Tauro-deoxycholic acid activates human αβγENaC by increasing open probability (Po) of active channels but not by recruiting additional near-silent channels. A, representative single-channel current recording obtained at a holding potential of −70 mV from an outside-out patch of an αβγENaC-expressing oocyte. Amiloride (Ami, 2 μm), t-DCA (250 μm), and chymotrypsin (Chym, 2 μg × ml−1) were present in the bath solution as indicated by the bars. The current level at which all channels are closed (C) was determined in the presence of amiloride. The different channel open levels are indicated by horizontal lines. The insets (1, 2, 3, and 4) show the indicated segments of the continuous current trace on an expanded time scale. Binned current amplitude histograms are shown on the right side of the insets and were obtained from the corresponding parts of the trace to calculate NPo values and single-channel current amplitude (i). The dotted lines in the insets indicate the channel open levels. The apparent number of active channels (apparent N) was determined by visual inspection of the traces. B, summary of data from similar experiments as shown in A (N = 4; n = 7). *, p < 0.05, **, p < 0.01, ***, p < 0.001, n.s., not significant; repeated measures one-way ANOVA with Bonferroni post hoc test. C, representative single-channel current recording without detectable single-channel activity before application of chymotrypsin obtained using the same experimental protocol as shown in A.