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

Abstract

We examined the effects of the protein kinase C (PKC) inhibitor, bisindolylmaleimide (BIM) (I), on voltage-dependent K + (K V) channels in rabbit coronary arterial smooth muscle cells using whole-cell patch clamp technique. BIM (I) reversibly and dose-dependently inhibited the K V currents with an apparent K d value of 0.27 μM. The inhibition of the K V current by BIM (I) was highly voltage-dependent between −30 and +10 mV (voltage range of channel activation), and the additive inhibition of the K V 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 K V channels. BIM (I) caused use-dependent inhibition of K V 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 + (K ATP), inward rectifier K + (K IR), Ca 2+-activated K + (BK Ca) 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 K V current and did not significantly alter the inhibitory effects of BIM (I) on the K V current. These results suggest that BIM (I) inhibits K V channels in a phosphorylation-independent, and voltage-, time- and use-dependent manner.