The protein kinase C inhibitor, bisindolylmaleimide (I), inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells

We examined the effects of the protein kinase C (PKC) inhibitor, bisindolylmaleimide (BIM) (I), on voltage-dependent K+ (KV) channels in rabbit coronary arterial smooth muscle cells using whole-cell patch clamp technique. BIM (I) reversibly and dose-dependently inhibited the KV currents with an apparent Kd value of 0.27 μM. The inhibition of the KV current by BIM (I) was highly voltage-dependent between −30 and +10 mV (voltage range of channel activation), and the additive inhibition of the KV current by BIM (I) was voltage-dependence in the full activation voltage range. The rate constants of association and dissociation for BIM (I) were 18.4 μM−1 s−1 and 4.7 s−1, respectively. BIM (I) had no effect on the steady-state activation and inactivation of KV channels. BIM (I) caused use-dependent inhibition of KV current, which was consistent with the slow recovery from inactivation in the presence of BIM (I) (recovery time constants were 856.95 ± 282.6 ms for control, and 1806.38 ± 110.0 ms for 300 nM BIM (I)). ATP-sensitive K+ (KATP), inward rectifier K+ (KIR), Ca2+-activated K+ (BKCa) channels, which regulate the membrane potential and arterial tone, were not affected by BIM (I). The PKC inhibitor, chelerythrine, and protein kinase A (PKA) inhibitor, PKA-IP, had little effect on the KV current and did not significantly alter the inhibitory effects of BIM (I) on the KV current. These results suggest that BIM (I) inhibits KV channels in a phosphorylation-independent, and voltage-, time- and use-dependent manner.