Fig. 4. Voltage dependence of activation of the Na⁺ currents, determined by I–V relationships for the Na⁺ currents elicited by the voltage steps. Smooth curves are simple Boltzmann functions. (A) V_1/2=–45.7 mV, k=–6.4 mV for perforated recording (filled circles), V_1/2=–46.1 mV, k=–5.2 mV for conventional recording (open circles). (B) V_1/2=–35.5 mV, k=–7.6 mV for 0.5 mmol l^–1 GTPS (filled triangles), V_1/2=–45.1 mV, k=–4.4 mV for 1 mmol l^–1 GDPßS (open triangles). For comparison, the broken line for conventional recording is plotted in B. The values are means ± S.E.M. obtained from 6–18 cells.