Figure 1. The accumulating current is I_Ks.

A, I_Ks activated by conventional seconds-long (3 s) depolarizations was increased by isoproterenol (Iso, 100 nM); administration of HMR 1556 (HMR, 500 nM) completely suppressed the current. The right panel shows the voltage protocol (applied at 0.1 Hz). B, repetitive depolarizations (voltage protocol on right) induced accumulation of an outward current that shows the same properties (increase by isoproterenol, block by HMR 1556) as I_Ks. The numbers in the baseline panel mark the 1st, 2nd, 99th and 100th depolarizations.