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. 2006 Nov;128(5):593–604. doi: 10.1085/jgp.200609648

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Copyright © 2006, The Rockefeller University Press

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Figure 9. — Effect of diC₈ PI(4,5)P₂ on the rundown of the voltage dependence of activation for HCN currents in sinoatrial node cells. (A) Representative whole-cell currents evoked by stepping the membrane from a holding potential of −35 mV to voltages ranging from −25 to −70 mV in 15-mV increments. The recordings were acquired 1 min (top) and 14 min (bottom) after membrane rupture in the absence (left) and in the presence (right) of 200 μM diC₈ PI(4,5)P₂ in the pipette solution. Hyperpolarizing test voltages indicated at right. (B) Mean tail current activation curves at 1 min (filled symbols) and 14 min (open symbols) in the absence (squares) and in the presence of 200 μM diC₈ PI(4,5)P₂ (circles). The curves show best fits of the Boltzmann equation. Mean values of parameters from Boltzmann fits of individual activation curves obtained 1 min after patch rupture in absence and presence of diC₈ PI(4,5)P₂ were, respectively, V_1/2 = −58.0 ± 1.5 mV (n = 8) and −58.3 ± 1.7 mV (n = 8, P > 0.05); s = 8.5 ± 0.7 mV and 7.8 ± 0.2 mV (P > 0.05). Mean parameters from Boltzmann fits obtained after 14 min of whole-cell recording in absence and presence of diC₈ PI(4,5)P₂ were, respectively, V_1/2 = −86.4 ± 2.8 mV (n = 6) and −72.4 ± 2.7 mV (n = 6, P < 0.05); s = 16.8 ± 1.3 mV and 12.9 ± 0.7 mV (P < 0.05). (C) Time course of rundown in V_1/2 during whole cell recordings in the absence (squares) and in the presence (circles) of 200 μM diC₈ PI(4,5)P₂. The two curves differ significantly at times indicated by asterisks. Values of V_1/2 for 1- and 14-min points from B. For 8-min points, mean activation parameters in absence and presence of diC₈ PI(4,5)P₂ were, respectively, V_1/2 = −70.9 ± 1.7 mV (n = 8) and −63.4 ± 1.6 mV (n = 8, P < 0.05) and s = 14.1 ± 0.3 mV and 10.9 ± 0.6 mV (P < 0.05). Data for B and C obtained from three animals. There was no difference in mean capacitance between the two groups (not depicted).