Kaempferol stimulates large conductance Ca 2+-activated K + (BK Ca) channels in human umbilical vein endothelial cells via a cAMP/PKA-dependent pathway

Abstract

Background and purpose: Kaempferol has been shown to possess a vasodilator effect but its mechanism of action remains unclear. In this study, experiments were carried out to study the effect of kaempferol on K + channels in endothelial cells. Experimental approach: K + channel activities in human umbilical vein endothelial cells (HUVECs) were studied by conventional whole cell and cell-attached patch-clamp electrophysiology. Key results: Kaempferol stimulated an outward-rectifying current in HUVECs in a dose-dependent manner with an EC 50 value of 2.5±0.02 μM. This kaempferol-induced current was abolished by large conductance Ca 2+-activated K + (BK Ca) channel blockers, such as iberiotoxin (IbTX) and charybdotoxin (ChTX), whereas the small conductance Ca 2+-activated K + (SK Ca) channel blocker, apamin, and the voltage-dependent K + (K V) channel blocker, 4-aminopyridine, had no effect. Cell-attached patches demonstrated that kaempferol increased the open probability of Bk Ca channels in HUVECs. Clamping intracellular Ca 2+ did not prevent kaempferol-induced increases in outward current. In addition, the kaempferol-induced current was diminished by the adenylyl cyclase inhibitor SQ22536, the cAMP antagonist Rp-8-Br-cAMP and the PKA inhibitor KT5720, but was not affected by the guanylyl cyclase inhibitor ODQ, the cGMP antagonist Rp-8-Br-cGMP and the PKG inhibitor KT5823. The activation of BK Ca channels by kaempferol caused membrane hyperpolarization of HUVECs. Conclusion and implications: These results demonstrate that kaempferol activates the opening of BK Ca channels in HUVECs via a cAMP/PKA-dependent pathway, resulting in membrane hyperpolarization. This mechanism may partly account for the vasodilator effects of kaempferol. © 2008 Nature Publishing Group All rights reserved.