Fig. 4.
Effects of bumetanide on STICs and slow-wave currents. Cells were studied using gramicidin-perforated, whole-cell voltage-clamp conditions. CaPSS was used as the external solution (Solution I), and K+-rich solution (Solution II, see Table 2) was used as the pipette solution. A: STICs occurred in cells held at −80 mV. HP = holding potential. Addition of bumetanide (40 μM) caused rapid reduction in STICs within a few minutes. Insets: STICs at an expanded time scale before and in the presence of bumetanide during the portions of the record designated by the red boxes. Slow-wave currents were evoked at a and b in the trace shown in A by stepping the cell from −80 mV to −35 mV. B: step protocol and the superimposed slow-wave current responses evoked by the step depolarizations, as indicated in A, at an expanded time scale. Under control conditions (black trace, a), depolarization evoked an inward current, and then a long-lasting tail current was observed when the cell was returned to the holding potential. Bumetanide (40 μM) changed characteristics of the slow-wave currents. At b (red trace), the initial current evoked by depolarization was outward, and the tail current was minimal. These observations indicate a progressive shift in ECl toward the holding potential in response to bumetanide. Blue lines denote the baseline of holding current at −80 mV.