XB-IMG-124588
Xenbase Image ID: 124588
|
Figure 6. Voltage dependence of intracellular PhTx block under low Na+ conditions. (A) Macroscopic current traces recorded in an inside-out patch containing CNGA1 channels in the absence or presence of 5 µM of intracellular PhTx in symmetrical 30 mM Na+. 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 = 4–8) by the indicated concentrations of intracellular PhTx is plotted against membrane voltage. Curves are fits of Eq. 3 to the three datasets simultaneously with Z1 fixed at 0. The best-fit parameters were: K1 = 1.04 ± 0.03 × 10−5 M, K2 = 2.03 ± 0.14 × 10−3, and Z2 = 2.08 ± 0.04. (C) Fraction of current not blocked (mean ± SEM; n = 8) by 1 µM of intracellular PhTx in the presence of 0.02 mM (filled circles) or 2 mM (open circles; taken from B) cGMP is plotted against membrane voltage. Curves are fits of Eq. 3 to both datasets simultaneously, with Z1 set to 0 and K1 common to both cGMP curves. The best-fit parameters were: K1 = 7.65 ± 0.22 × 10−6 M for both cGMP concentrations; K2 = 1.29 ± 0.08 × 10−2 and Z2 = 1.92 ± 0.05 for 0.02 mM cGMP; and K2 = 1.72 ± 0.18 × 10−3 and Z2 = 2.29 ± 0.06 for 2 mM cGMP. (D) Kinetics of depolarization-induced CNGA1 block by intracellular PhTx in 30 mM Na+. Natural logarithm of kon, determined as in Fig. 3, at four concentrations (0.03, 0.1, 0.3, and 1 µM; n = 6) of intracellular PhTx is plotted against membrane voltage. The plot is fitted with the equation ln kon = ln kon (0 mV) + zonVF/RT, yielding kon (0 mV) = 8.42 ± 0.68 × 108 M−1s−1 and zon = 0.14 ± 0.01. (E) Kinetics of hyperpolarization-induced recovery from CNGA1 block by intracellular PhTx in 30 mM Na+. Natural logarithm of koff, determined as in Fig. 4, at four concentrations (0.1, 0.3, 0.6, and 1 µM; n = 6) of intracellular PhTx is plotted against membrane voltage. The plot is fitted with the equation ln koff = ln koff (0 mV) − zoffVF/RT, yielding koff (0 mV) = 27 ± 2 s−1 and zoff = 1.10 ± 0.02. 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 |