Tungstate-Targeting of BKαβ1 Channels Tunes ERK Phosphorylation and Cell Proliferation in Human Vascular Smooth Muscle

Despite the substantial knowledge on the antidiabetic, antiobesity and antihypertensive actions of tungstate, information on its primary target/s is scarce. Tungstate activates both the ERK1/2 pathway and the vascular voltage-and Ca2+-dependent large-conductance BK alpha beta(1) potassium channel, which modulates vascular smooth muscle cell (VSMC) proliferation and function, respectively. Here, we have assessed the possible involvement of BK alpha beta(1) channels in the tungstate-induced ERK phosphorylation and its relevance for VSMC proliferation. Western blot analysis in HEK cell lines showed that expression of vascular BK alpha beta(1) channels potentiates the tungstate-induced ERK1/2 phosphorylation in a G(i/o) protein-dependent manner. Tungstate activated BK alpha beta(1) channels upstream of G proteins as channel activation was not altered by the inhibition of G proteins with GDP beta S or pertussis toxin. Moreover, analysis of Gi/o protein activation measuring the FRET among heterologously expressed G(i) protein subunits suggested that tungstate-targeting of BK alpha beta(1) channels promotes G protein activation. Single channel recordings on VSMCs from wild-type and beta(1)-knockout mice indicated that the presence of the regulatory beta(1) subunit was essential for the tungstate-mediated activation of BK channels in VSMCs. Moreover, the specific BK channel blocker iberiotoxin lowered tungstate-induced ERK phosphorylation by 55% and partially reverted (by 51%) the tungstate-produced reduction of platelet-derived growth factor (PDGF)induced proliferation in human VSMCs. Our observations indicate that tungstate-targeting of BK alpha beta(1) channels promotes activation of PTX-sensitive G(i) proteins to enhance the tungstate-induced phosphorylation of ERK, and inhibits PDGF-stimulated cell proliferation in human vascular smooth muscle.