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Figure 5. Voltage-dependent block by intracellular PhTx. (A) Macroscopic current traces recorded from an inside-out patch containing CNGA1 channels in the absence or presence of 0.3 µM of intracellular PhTx. Currents were activated with 2 mM of intracellular cGMP and elicited with the voltage protocol shown. Dotted line indicates 0 current level. (B) Fraction of current not blocked (mean ± SEM; n = 5–10) by intracellular PhTx is plotted against membrane voltage. Curves are fits of a single Boltzmann function to the four datasets simultaneously with parameters: appKd (0 mV) = 8.58 ± 0.38 × 10−7 M and Z = 2.67 ± 0.04. (C) Kinetics of depolarization-induced CNGA1 block by intracellular PhTx. Natural logarithm of second-order rate constant kon, determined as in Fig. 3, at three concentrations of intracellular PhTx (0.3, 1, and 10 µM; n = 8) is plotted against membrane voltage. The plot is fitted with the equation ln kon = ln kon (0 mV) + zonVF/RT, yielding kon (0 mV) = 4.23 ± 0.34 × 107 M−1s−1 and zon = 0.23 ± 0.01. (D) Kinetics of hyperpolarization-induced recovery from CNGA1 block by intracellular PhTx. Natural logarithm of koff, determined as in Fig. 4, at three concentrations of intracellular PhTx (0.1, 0.3, and 1 µM; n = 5) is plotted against membrane voltage. The plot is fitted with the equation ln koff = ln koff (0 mV) − zoffVF/RT, yielding koff (0 mV) = 33 ± 1 s−1 and zoff = 1.60 ± 0.01. Image published in: Martínez-François JR and Lu Z (2010) © 2010 Martínez-François and Lu. This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View

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