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. 2005 Aug 25;568(Pt 2):371–380. doi: 10.1113/jphysiol.2005.093161

Figure 3. Ih blockers decrease open probabilities, increase first-latencies and slightly decrease conductance of single h-channels.

Figure 3

A, representative traces of channel openings elicited by hyperpolarization steps from −30 mV to −90 mV in control, 50 μm ZD7288 and 1 mm CsCl conditions. Based on inside-out patch configuration, positive (upward) deflections represent inward current. Closed state is indicated by c and dashed line. B, ZD7288 (50 μm) reduced Pos in an apparent voltage-dependent manner with greatest inhibition at depolarized potentials. In contrast, inhibition by CsCl (1 mm) was greatest at hyperpolarized potentials. (ZD7288 bath applied: n = 65–168 sweeps from 7 to 14 patches; CsCl included in the pipette solution: n = 38–96 sweeps from 4 to 10 patches.) C, cumulative frequency distribution histograms of the latency to first channel openings during a −70 mV step demonstrated the dramatic increases in latencies caused by 50 μm ZD7288 and 1 mm CsCl (bin width = 10 ms). Sweeps with no channel openings were included (control, n = 201 sweeps from 8 patches; ZD7288, n = 137 sweeps from 14 patches; CsCl, n = 96 sweeps from 10 patches). D, ZD7288 and CsCl slightly reduced the channel conductance to 8.0 and 8.4 pS (r= 0.78 and 0.98), respectively. Dashed line is the control I–V fit from Fig. 2. Voltages and current amplitudes are corrected for patch configuration. Compared to control patches (Fig. 2 legend), the amplitude histograms of pooled events from all inhibitor-exposed patches that did have openings had lower Gaussian means at all voltage steps, but were not significantly different from control (P > 0.05; unpaired t test). Channel openings of ZD7288-exposed patches had mean amplitudes of −0.43 ± 0.07, −0.49 ± 0.25, −0.59 ± 0.13, −0.62 ± 0.19, and −0.75 ± 0.07 pA at −60, −70, −80, −90, and −100 mV, respectively, giving a conductance of 7.6 pS. Channel openings of CsCl-exposed patches had mean amplitudes of −0.44 ± 0.03, −0.50 ± 0.04, −0.55 ± 0.05, −0.63 ± 0.08, −0.73 ± 0.03, −0.82 ± 0.05 and 0.99 ± 0.04 pA at −50, −60, −70, −80, −90, −100 and −120 mV, respectively, giving a conductance of 8.0 pS (Gaussian mean ±s.d.; slope conductance by linear regression, r= 0.99 and 0.995).