Direct modulation of Ca2+-activated K+ current by H-89 in rabbit coronary arterial smooth muscle cells

The effects of H-89, a potent and selective inhibitor of protein kinase A (PKA) on Ca2+-activated K+ (BKCa) channels in coronary arterial smooth muscle cells were examined using a patch-clamp technique. In inside-out configuration, H-89 increased the NPo of the BKCa channel, but it reduced the dwell time of BKCa currents. In whole-cell configuration, H-89 markedly increased BKCa currents in a concentration-dependent manner. The EC50 was 0.470 ± 0.0741 μM based on dwell time, 0.582 ± 0.0691 μM based on the NPo, and 0.519 ± 0.0295 μM based on the whole-cell current, respectively. H-85, which is an inactive form of H-89, increased BKCa 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 BKCa currents and did not significantly alter the stimulatory effects of 1 μM H-89. These findings suggest that H-89 increases the BKCa current independently of PKA.