Xenbase Image ID: 121715

Figure 14. Removal of inactivation by trypsin shifts the V0.5 for activation at low Ca2+ to higher values and results in a weaker apparent voltage dependence of activation. In A, traces show α + β3b currents activated with the indicated voltage-protocol before (left column) and after (right column) removal of inactivation by brief trypsin application to the cytosolic face of the inside-out patch. Concentrations were 0, 1, and 10 μM Ca2+ as indicated. In B, normalized tail current G-V curves are plotted for a different set of five α + β3b patches before (open symbols) and after (solid symbols) trypsin application for 0 (•, ○), 1 (▪, □), 10 (♦, ⋄), and 300 (▴, ▵) μM Ca2+. Solid lines are fits of . Before trypsin, values for V0.5 were 132.3, 108.9, 21.1, and −51.2 mV for 0, 1, 10, and 300 μM Ca2+, respectively. After trypsin, V0.5 values were 170.2, 148.0, 50.1, and −41.3 mV for 0, 1, 10, and 300 μM, respectively. Average value of k before trypsin for this set of patches was 16.5 ± 1.3 mV (mean ± SD) and, after trypsin, 23.9 ± 2.6 mV. The solid line with smaller circles was the fit of to currents obtained at 10 and 300 μM Ca2+. For 10 μM Ca2+, Gmax1 = 60.0, k1 = 14.8 mV, V10.5 = 34.3 mV, Gmax2 = 40.0, k2 = 26.6 mV, and V20.5 = 89.3 mV. For 300 μM, Gmax1 = 70.2, k1 = 17.7 mV, V10.5 = −54.9 mV, Gmax2 = 29.8, k2 = 47.1 mV, and V20.5 = 53.2 mV. In C, mean values for V0.5 obtained from fits of at four different [Ca2+] are plotted as a function of [Ca2+] for the five patches with α + β3b currents shown in B both before (•) and after (○) trypsin was applied to remove inactivation. Error bars are SD. The V0.5 for four patches (♦) expressing only α alone was also determined from the same batch of oocytes. Image published in: Zeng XH et al. (2001) © 2001 The Rockefeller University Press. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View

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