Introduction
KCNQ-encoded KV7 channels are key regulators of arterial
reactivity. Of the five KCNQ subtypes, KCNQ4 is the most predominantly
expressed in the vasculature, followed by KCNQ5 then KCNQ1, with little
to no contribution from KCNQ2/3 (Ng et al., 2011; Ohya, Sergeant,
Greenwood, & Horowitz, 2003; Yeung et al., 2007). In human and rodent
blood vessels KV7 channels contribute to resting tone
(Ohya et al. , 2003; Yeung et al. , 2007; Ng et al. ,
2011, Mackie et al., 2008) whereby KV7 blockers like
linopirdine or XE991 produce contractions or enhance vasoconstrictor
responses. In addition, a range of compounds like retigabine or S-1 that
increase the activity of KV7.2-7.5 are effective
relaxants of pre-contracted arteries. KV7 channels are
also functional end targets for a myriad of endogenous vasoactive
responses. Channel activity is impaired during PKC-mediated
vasoconstriction (L. I. Brueggemann et al., 2006) and enhanced as a
result of cGMP and cAMP dependent receptor-mediated vasodilatations
(e.g. Chadha et al. , 2012; Khanamiri et al., 2013; Stott, Jepps
and Greenwood, 2014; Stott et al. , 2015; Mani et al. ,
2016; Brueggemann et al. , 2018). To date, vascular studies on
KV7 channels have focused predominantly on vascular
smooth muscle cells (VSMCs), and as a result it is currently unclear
whether endothelial cell (EC) KV7 channels exist and if
so, what their functional role may be.
The inner layer of blood vessels is comprised of ECs, which constitute a
paracrine signaling platform that lines all blood vessels. These cells
regulate VSMC contractility, vascular resistance and ultimately blood
flow through the release of nitric oxide (NO), prostacyclin,
epoxyeicosatrienoic acid and others as well as the generation and spread
of endothelium-derived hyperpolarization (EDH) (McGuire, Ding, &
Triggle, 2001). Myoendothelial projections within fenestrations (holes)
of the internal elastic lamina (IEL) facilitate the presence of
myoendothelial gap junctions (MEGJs) at a proportion of such sites
(~50% in adult rat
1st-3rd order ‘large’ mesenteric
arteries; MA; (Sandow et al., 2009). Such junctions facilitate
heterocellular electrochemical coupling via connexins at junction sites
(Sandow, Senadheera, Bertrand, Murphy, & Tare, 2012). Ultimately, MEGJs
enable EC-derived signaling pathways via the flow of both small
molecules <~1 kDa and selective currents
between cell types. Within rat MA EC-derived vasorelaxant microdomain
signaling cascades, previous data has implicated fundamental roles for
small/intermediate conductance calcium-activated potassium channels
(SKCa and IKCa, respectively; (Sandow,
Neylon, Chen, & Garland, 2006); Dora et al., 2008 Circ Res), transient
receptor potential canonical type 3 channels (Senadheera et al., 2012),
inositol-1,3,4 trisphosphate receptor/s (Sandow CEPP 2009), and inwardly
rectifying potassium channels (KIR2) (Goto, Rummery,
Grayson, & Hill, 2004). More recently, within mouse MA,
KIR2.1 has been identified as a propagator of EC derived
signals, acting as a hyperpolarization ‘booster’ (Sonkusare, Dalsgaard,
Bonev, & Nelson, 2016).
Despite the contribution of KV7 channels to baseline
VSMC tension and receptor-mediated responses, their expression and
function within ECs remains relatively unknown. This study shows that
KV7 channels are expressed in rat mesenteric ECs and
contribute to both KV7 activator mediated vasorelaxation
via a novel functional interaction with KIR2 channels
and endothelial nitric oxide synthase (eNOS)-dependent carbachol
(CCh)-mediated vasorelaxation.