Arachidonic acid activation of BKCa (Slo1) channels associated to the β1-subunit in human vascular smooth muscle cells
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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 Ca2+- 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 accelerates the kinetics of the voltage channel activation by a fourfold reduction in latencies to first channel opening. When AA was 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 probably by interacting with the β1-subunit, without modifying the channel voltage sensitivity. Since BKCa 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.
KeywordsPUFAs Fatty acid Omega-6 polyunsaturated fatty acid Human umbilical artery Patch-clamp Single channel
The authors wish to thank Ms. Anabel Poch and the staff of the Instituto Central de Medicina for the collection of umbilical cords. This study was financially supported by grant PIP 0202 from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina, and by FONDECYT Grants 1120802, Anillo ACT 1104 (to Carlos Gonzalez), and the Chile–Argentina exchange grant 2011-665 CH/11/12 (to Veronica Milesi and Carlos Gonzalez from the Centro Interdisciplinario de Neurociencia de Valparaíso (The Interdisciplinary Center for Neuroscience in Valparaiso), a Millennium Institute.
Dr. Jesica Raingo generously contributed to this work by providing HEK293T cells, eGFP, and vector. We are grateful to Dr. Alejandro Rebolledo for critical feedback on the manuscript and to Francina Agosti for her helpful assistance in cell culturing and transfection.
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