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 mu M based on dwell time, 0.582 +/- 0.0691 mu M based on the NPO, and 0.519 +/- 0.0295 mu M 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 mu M) had little effect on BKCa currents and did not significantly alter the stimulatory effects of 1 mu M H-89. These findings suggest that H-89 increases the BKCa current independently of PKA. (c) 2006 Elsevier Inc. All rights reserved.