FIGURE 5.

Native I_Ks recorded from guinea pig cardiac myocytes lacks ZnPy sensitivity. A, the total current (I_total) elicited by a series of depolarization steps from -70 mV to +70 mV in 10-mV increments in normal Tyrode's solution, which includes 140 mm Na⁺, 5.4 mm K⁺, and 1.8 mm Ca²⁺, is shown. B, the current recorded in a modified Na⁺-free external solution supplemented with 50 μm La³⁺ to block I_Kr and 5 μm nifedipine to block I_Ca is shown. C, the currents recorded in the modified external solution were inhibited by 100 μm I_Ks selective inhibitor chromanol 293B. D, the currents recorded in the same cells in B after application of 10 μm ZnPy are shown. E, the histogram shows that 10 μm ZnPy did not increase the native I_Ks amplitude. F, G-V curves of native I_Ks in the absence or presence of 10 μm ZnPy are shown. G, the histogram shows that 10 μm ZnPy did not affect the deactivation rate of the native I_Ks.