Figure 9.

Effects of ZD6169 on the unitary Ba²⁺ current in pig urethra at a holding potential of −30 mV. High K⁺ (142 mM) solution was superfused in the bath and high Ba²⁺ (90 mM) solution in the pipette. Bay K8644 (1 μM) had been included in the pipette solution. (a) Application of 100 μM ZD6169 (5 min duration) reduced the activity of the 1.9 pA Ba²⁺ channel. After removal of ZD6169, 3 min later, application of nifedipine (10 μM) abolished channel activity. Lower traces show expansions of the upper trace (1 kHz filtration; 80 μs digital sampling interval). The open horizontal bars in the absence and presence of 100 μM ZD6169 indicate the duration (2 min) of the traces analysed in (b). The dashed line indicates the current when the channel is not open. (b) All-point amplitude histograms in the absence (obtained during the last 2 min just before application of ZD6169) and presence of 100 μM ZD6169 (obtained during 2 min of a 5 min application). Continuous lines in the histograms are theoretical curves fitted with the Gaussian distribution, by the least-squares method. The abscissa scales show the amplitude of the current (pA) and the ordinate scales show the percentage value of the probability density function (per cent) for the recording period (2 min). (c) Each column shows the relative level of the activity of the 1.9 pA Ba²⁺ channel (mean value with+s.d.) when the mean open probability of the channel activity was normalized as one just before application of each concentration of ZD6169 (n=5).