Direct modulation of Ca 2+-activated K + current by H-89 in rabbit coronary arterial smooth muscle cells

Abstract

The effects of H-89, a potent and selective inhibitor of protein kinase A (PKA) on Ca 2+-activated K + (BK Ca) channels in coronary arterial smooth muscle cells were examined using a patch-clamp technique. In inside-out configuration, H-89 increased the NP o of the BK Ca channel, but it reduced the dwell time of BK Ca currents. In whole-cell configuration, H-89 markedly increased BK Ca currents in a concentration-dependent manner. The EC 50 was 0.470 ± 0.0741 μM based on dwell time, 0.582 ± 0.0691 μM based on the NP o, and 0.519 ± 0.0295 μM based on the whole-cell current, respectively. H-85, which is an inactive form of H-89, increased BK Ca currents, similar to the result of H-89. The other PKA inhibitors (Rp-8-CPT-cAMPs and KT 5720) and protein phosphatase inhibitor (okadaic acid, 1 μM) had little effect on BK Ca currents and did not significantly alter the stimulatory effects of 1 μM H-89. These findings suggest that H-89 increases the BK Ca current independently of PKA.