Figure 6.

Effect of a partial I_K block and high [Mg²⁺]_o on the action potential. (A) APs recorded at 36 °C using K⁺-containing intra- and extracellular solutions under perforated patch conditions and initially superfused with control extracellular solutions containing 0.9-mM [Mg²⁺]. A combination of HMR1556 (100 nM) and E4031 (500 nM) was then added in 0.9-mM [Mg²⁺]_o before applying 7.2-mM [Mg²⁺]_o together with the drugs. (B) Summary data of the AP duration (APD) at 30%, 50%, and 90% repolarization (APD₃₀, APD₅₀, and APD₉₀, respectively) measured under the control conditions (unshaded column) in the presence of the I_K inhibitors (grey column) and in the presence of the I_K inhibitors but with the [Mg²⁺]_o raised to 7.2 mM (red column). * p < 0.05 for the presence vs. absence of the I_K inhibitors (in 0.9-mM [Mg²⁺]_o). # p < 0.05 for 7.2-mM vs 0.9-mM [Mg²⁺]_o in the presence of the I_K inhibitors (n = 4). Notice the shortening of the APD₅₀ and APD₉₀ by high [Mg²⁺]_o in the presence of the I_K blockers.