Figure 6.

Voltage-dependent phosphatase activity by FRET analysis with F-TAPP, a PI(3,4)P₂ sensor in Xenopus oocyte. (A) Representative traces of F-TAPP YFP/CFP ratio signal measured at 0, 50, 100, and 150 mV from top to bottom. Depolarizing step shown at top of traces was applied from a holding potential of −60 mV to indicated value for 5 s. Dotted line in each trace indicates the time point (at 4 s after the beginning of depolarization) for calculating ΔFRET. Signal from oocytes with WT Ci-VSP and without Ci-VSP is shown as black and purple trace, respectively. (B) FRET signal as the shift from the baseline measured at 4 s after initiation of step to 0, 50, 100, and 150 mV from top to bottom. The number of recordings is shown for WT and mutants. Data are presented as mean ± SE. (C) Decrease of FRET signal at 4 s after initiation of voltage step for each mutant plotted against voltage. Data at 25 and 75 mV are shown in Fig. S6. Each trace from 0 to 150 mV was obtained from the same oocytes. In (B) and (C), data are presented as mean ± SE. ^∗p < 0.05; ^∗∗p < 0.01; ^∗∗∗p < 0.001; n.s., statistically not significant, one-way ANOVA followed by Dunnett’s test. Sample size is as described in (B) and Fig. S7B.