Arachidonic acid activation of BKCa (Slo1) channels associated to the β1-subunit in human vascular smooth muscle cells

Abstract

Arachidonic acid (AA) is a polyunsaturated fatty acid involvedin a complex network of cellsignaling. Itis well known that this fatty acid can directly modulate several cellu- lar target structures, among them, ion channels. We explored the effects of AA on high conductance Ca 2+ - and voltage- dependent K + channel (BKCa) in vascular smooth muscle cells (VSMCs) where the presence of β1-subunit was functionally demonstrated by lithocholic acid activation. Using patch- clamp technique, we show at the single channel level that 10 μM AA increases the open probability (Po) of BKCa channels tenfold, mainly by a reduction of closed dwell times. AA also induces a left-shift in Po versus voltage curves without modifying their steepness. Furthermore, AA acceler- atesthekineticsofthevoltagechannelactivationbyafourfold reduction in latencies to first channel opening. When AAwas tested on BKCa channel expressed in HEK cells with or without the β1-subunit, activation only occurs in presence of the modulatory subunit. These results contribute to highlight the molecular mechanism of AA-dependent BKCa activation. We conclude that AA itself selectively activates the β1- associated BKCa channel, destabilizing its closed state proba- bly by interacting with the β1-subunit, without modifying the channel voltage sensitivity. Since BKCa channels physiologi- cally contribute to regulation of VSMCs contractility and blood pressure, we used the whole-cell configuration to show that AA is able to activate these channels, inducing significant cell hyperpolarization that can lead to VSMCs relaxation.