Figure 3. Inhibition of HERG tail current by various concentrations of Ba²⁺.

Results are means ±s.e.m. for 5, 5, 5 and 4 oocytes studied before and after 1, 10, 500 μm and 2 mm Ba²⁺, respectively. Tail currents were recorded returning to the V_h of -80 mV following 2 s steps to the voltages indicated. Current amplitudes were estimated by fitting the deactivation phase of the tails to biexponential functions and extrapolating back to the beginning of the repolarizing step. All currents were normalised to the maximum control current amplitude (* P < 0.05, ** P < 0.01, *** P < 0.001 vs. control). Data were fitted to Boltzman functions (I_HERG= (1 + exp [(V_½+V_t/k)])⁻¹) where V_½ is the half-activation voltage, V_t is the test voltage applied and k is the slope factor. V_½ and k (in mV) estimated from the fits were: -18.9 ± 0.5, 9.7 ± 0.5; -17.7 ± 1, 11.1 ± 1.0; -17.2 ± 0.7, 10.5 ± 0.7; -16.3 ± 0.7, 10.1 ± 0.7 under control conditions and -16.0 ± 0.5, 8.7 ± 0.4; -10.7 ± 1, 9.0 ± 1.0; -4.4 ± 0.8, 8.9 ± 0.7; 1.0 ± 1.7, 9.6 ± 1.4 mV for 1, 10, 500 μm and 2 mm Ba²⁺, respectively.