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

Figure 4. cAMP increases open probabilities, decreases first-latencies and does not effect conductance of single h-channels.

Figure 4

A, representative traces of channel openings elicited by hyperpolarization steps from −30 mV to −90 mV in control and 10 μm 8Br-cAMP conditions. Based on inside-out patch configuration, positive (upward) deflections represent inward current. Closed state is indicated by c and dashed line. B, 8Br-cAMP (10 μm) increased Po values, but every patch was lost by −90 mV. Therefore, we assumed that the peak Po would be near the control peak (0.8) by −120 mV and fitted the data with a Boltzmann equation resulting in V1/2 of −76.6 ± 2.5 mV and slope −7.8 ± 2.2 mV (n = 12–70 sweeps from 2 to 6 patches). The control V1/2 was −81.3 ± 1.8 mV and slope −13.3 ± 1.9 mV (dashed line). C, similar to control, 10 μm 8Br-cAMP-exposed channels had a slope conductance of 9.4 pS. Dashed line is the control I–V fit from Fig. 2B. Voltages and current amplitudes are corrected for patch configuration. The Gaussian-fit histograms of pooled events from all 8Br-cAMP patches (not shown) resulted in current amplitudes of −0.21 ± 0.07, −0.30 ± 0.09, −0.43 ± 0.06, −0.44 ± 0.04, −0.54 ± 0.06, −0.65 ± 0.02, and −0.79 ± 0.03 pA at −30, −40, −50, −60, −70, −80 and −90, mV, respectively, giving a conductance of 9.1 pS (Gaussian mean ±s.d.; slope conductance by linear regression, r= 0.99; P > 0.05 versus control (Fig. 2 legend) by unpaired t test). D, averaged latencies to first channel openings after a voltage step decreased with hyperpolarization, but were not decreased significantly by 10 μm 8Br-cAMP (P > 0.05 versus control by unpaired t test). Only steps activating channels were included (control, n = 35–151 sweeps from 5 to 8 patches; 8Br-cAMP, n = 12–29 sweeps from 2 to 6 patches). E, cumulative frequency distribution histograms of the latency to first channel openings during a −70 mV step demonstrated 8Br-cAMP increased probabilities of first openings for latencies ≤ 1 s, but did not modulate cumulative probabilities of latencies ≥ 1 s (bin width = 10 ms). Sweeps with no channel openings were included (control, n = 201 sweeps from 8 patches; 8Br-cAMP, n = 39 sweeps from 4 patches).