Fig. 7
Stimulatory effects of SAF on window INa [INa(W)] induced by an ascending ramp voltage Vramp in GH3 cells. For the experiments, the test cells were maintained at −80 mV and subjected to Vramp ranging from −100 to +40 mV over 200 ms (ramp speed of 0.7 mV/ms). (A) INa(W) trace in the absence (a, blue) and presence (b, red) of 10 μM SAF. The inset indicates the Vramp protocol, and the downward deflection indicates inward-directed current. The continuous gray lines corresponding to the untreated or SAF-treated (10 μM) cells were fitted (least-squares minimization) with the Boltzmann equation. The values of V1/1 and q (apparent gating charge) induced by ascending Vramp over 200 ms in the absence (blue) of SAF were, respectively, −34 mV and 2.1 e; the corresponding values in the presence (red) of 10 μM SAF were −38 mV and 2.8 e, respectively. (B) Summary graph illustrating the effects of SAF (3 and 10 μM) and SAF (10 μM) plus Ran (10 μM) on the Δarea of INa(W) in GH3 cells (mean ± standard error of the mean; n = 7 for each point). The value of Δarea was measured at a voltage ranging from −80 and +40 mV, which corresponded to INa(W) induced by the ascending Vramp. The statistical analyses were done by ANOVA-1, P < 0.05, followed by post-hoc Fisher’s least-significant different test, P < 0.05. *Significantly different from the control (P < 0.05), **significantly different from the SAF (3 μM) alone group (P < 0.05), and +significantly different from the SAF (10 μM) alone group (P < 0.05). (C) Summary graph illustrating the effects of SAF (3 and 10 μM) and SAF plus Ran (10 μM) on ΔG0 (mean ± standard error of the mean; n = 7 for each point). The estimation of ΔG0 for the induction of instantaneous INa(W) is described in the Materials and Methods section. Notably, increasing the concentration of SAF increased ΔG0 in GH3 cells; further addition of Ran effectively reversed the SAF-induced increase in ΔG0. The statistical analyses were done by ANOVA-1, P < 0.05, followed by post-hoc Fisher’s least-significant different test, P < 0.05.*Significantly different from the control (P < 0.05), **significantly different from the SAF (3 μM) alone group (P < 0.05), and +significantly different from the SAF (10 μM) alone group (P < 0.05)