Arachidonic acid activation of BK^sub Ca^ (Slo1) channels associated to the [beta]^sub 1^-subunit in human vascular smooth muscle cells

Arachidonic acid (AA) is a polyunsaturated fatty acid involved in a complex network of cell signaling. It is well known that this fatty acid can directly modulate several cellular target structures, among them, ion channels. We explored the effects of AA on high conductance Ca^sup 2+^- and voltage-dependent K^sup +^ channel (BK^sub Ca^) in vascular smooth muscle cells (VSMCs) where the presence of [beta]^sub 1^-subunit was functionally demonstrated by lithocholic acid activation. Using patch-clamp technique, we show at the single channel level that 10 [mu]M AA increases the open probability (Po) of BK^sub Ca^ 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 accelerates the kinetics of the voltage channel activation by a fourfold reduction in latencies to first channel opening. When AA was tested on BK^sub Ca^ channel expressed in HEK cells with or without the [beta]^sub 1^-subunit, activation only occurs in presence of the modulatory subunit. These results contribute to highlight the molecular mechanism of AA-dependent BK^sub Ca^ activation. We conclude that AA itself selectively activates the [beta]^sub 1^-associated BK^sub Ca^ channel, destabilizing its closed state probably by interacting with the [beta]^sub 1^-subunit, without modifying the channel voltage sensitivity. Since BK^sub Ca^ channels physiologically 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.[PUBLICATION ABSTRACT]