XB-IMG-122302
Xenbase Image ID: 122302
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Figure 10. . Prepulse-dependent shift of G(V). (A and B) Ionic currents through spHCN channels in response to voltage steps in 10-mV increments between +50 mV and â100 mV, from VH = â10 mV with (A) or without (B) a 50-ms prepulse to â100 mV. Tail currents at +50 mV. 100-K bath solution. The relatively large âleakâ currents seen in A and B are a property of spHCN channels (compare recording in Fig. 4, which is the result of a subtraction of identical recordings executed on the same cell before and after an application of the HCN-channel blocker ZD7288; even in these ZD7288-subtracted currents, there was an instantaneous current component when the voltage was stepped from a 0-mV holding potential). (C) G(V) curves for spHCN after prepulses with durations of 0 (â¡), 10 (â), 25 (âµ), 50 (â¿), and 100 (â) ms, measured from an instantaneous tail current at +50 mV. Fitted to G(V) = A + B/(1 + exp(âze0(V â V1/2)/kT). V1/2 = â43, â30, â12, â3, +2. z = 1.59, 1.33, 1.37, 1.87, and 2.10. 100-K bath solution. (D) V1/2 versus prepulse duration from C, fitted with a single exponential with Ï = 24 ms. (EâH) Computer simulations of G(V) shifts for the models in Fig. 5. Holding potential is 0 mV followed by prepulses to â100 mV for 0, 75, 150, 225, 300, and 375 ms (from left to right), followed by equilibrium steps of 200 ms to the voltages indicated on the x axis. Compared with the other models, the four-state model exhibits the largest and the slowest shifts. (I) G(V) shifts for the four-state (open symbols) and the two-state (closed symbols) models for different prepulse potentials (circle, â180 mV; triangle, â140 mV; square, â100 mV; diamond, â60 mV). The continuous curves are best fits of single exponentials through origin. (J) Time constants from I. Note that the time constants from the four-state model, in contrast to the two-state model, levels out as was found in the experiments. Image published in: Männikkö R et al. (2005) Copyright © 2005, The Rockefeller University Press. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View |