FIGURE 4.
Chenodeoxycholic acid does not stimulate hyperactive δβγENaC in outside-out patches but reduces single-channel current amplitude. A, representative single-channel current recording obtained at a holding potential of −70 mV from an outside-out patch with only one active δβγENaC channel. Amiloride (Ami, 10 μm), CDCA (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 the channel is closed (C) was determined in the presence of amiloride. The open and closed channel 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. Asterisks indicate single-channel events shown on the right side of the corresponding inset with higher time resolution. Binned current amplitude histograms (not shown) were obtained from the current traces depicted in the insets and were used to calculate NPo and single-channel current amplitude (i). With only one active channel in the patch, the NPo value corresponds to Po. The dotted lines in the insets indicate the closed and open channel levels. B, summary of Po values from similar experiments as shown in A with only one active channel in the patch (N = 6; n = 6). n.s., not significant, paired t test. C, summary of i values from similar experiments as shown in A but including experiments with more than one channel in the patch (N = 7; n = 7). ***, p < 0.001, n.s., not significant, repeated measures one-way ANOVA with Bonferroni post hoc test.