Inhibitory Effect of Thiopental on Ultra-rapid Delayed Rectifier K+ Current in H9c2 Cells

Using the whole-cell voltage clamp technique, we investigated the effects of thiopental on membrane currents in H9c2 cells, a cell line derived from embryonic rat heart. Thiopental blocked a rapidly activating, very slowly-inactivating ultra-rapid type IKur-like outward K+ current in a concentration-dependent manner. The half-maximal concentration (IC50) of thiopental was 97 µM with a Hill coefficient of 1.2. The thiopental-sensitive current was also blocked by high concentrations of nifedipine (IC50 = 9.1 µM) and 100 µM chromanol 293B, a blocker of slowly activating delayed rectifier K+ current (IKs), but was insensitive to E-4031, an inhibitor of rapidly activating delayed rectifier K+ current (IKr). TEA (tetraethylammonium) at 5 mM and 4-AP (4-aminopiridine) at 1 mM reduced the K+ current to 30.8 ± 12.2% and 20.5 ± 6.5% of the control, respectively. Using RT-PCR, we detected mRNAs of Kv2.1, Kv3.4, Kv4.1, and Kv4.3 in H9c2 cells. Among those, Kv2.1 and Kv3.4 have IKur-type kinetics and are therefore candidates for thiopental-sensitive K+ channels in H9c2 cells. This is the first report showing that thiopental inhibits IKur. This effect of thiopental may be involved in its reported prolongation of cardiac action potentials. Keywords:: thiopental, ultra-rapid delayed-rectifier K+ current, patch clamp, H9c2 cell, Kv2.1 channel