Differential Regulation of KV7 Channels by cGMP-linked Vasodilator Responses in the Rat Aorta

J B Stott1, T A Jepps1,2, E V Leighton1, I A Greenwood1,2. 1St George's University of London, London, UK, 2University of Copenhagen, Copenhagen, Denmark

KV7 channels are key regulators of vascular tone, and have been shown to be involved in endogenous vasodilator responses (1). However, the intracellular signalling mechanisms by which vasoactive substances activate KV7 channels are yet to be elucidated. Moreover, there is no information on the role of Kv7 channels in cGMP-mediated relaxations. Natriuretic peptides and the NO donor sodium nitroprusside are vasodilators which can act through stimulating cyclic GMP, and subsequent activation of both protein kinases A and G (PKA and PKG). The natriuretic peptides atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) stimulate cGMP via stimulation of guanylate cyclase linked natriuretic peptide receptors (NPR-A and NPR-B, respectively), although both can also activate a third natriuretic peptide receptor (NPR-C), which activates G-protein βγ subunits. Therefore, the aim of this study was to investigate a possible role for KV7 channels in responses of rat aorta to the natriuretic peptides ANP and CNP and to the nitric oxide donor sodium nitroprusside (SNP) and to define the signalling mechanisms involved in these responses.

Segments of aorta were isolated from male Wistar rats (200-225g) and mounted on pins in a myograph (Danish Myograph Technologies) for isometric tension recording. Aortae were precontracted with 3μM methoxamine and relaxant dose responses to ANP, CNP and SNP were determined in the absence or presence of the KV7 blocker linopirdine (10μM),or inhibitors of PKA (KT5720, 1 μM), PKG (KT5823, 1 μM) and βγ subunits (Gallein, 100 μM). The rat aorta displayed relaxant responses to ANP (EC50 0.91 ± 0.09nM), CNP (EC50 62.6 ± 10.9nM) and SNP (EC50 11.33 ± 1.3nM) which were significantly attenuated in the presence of linopirdine (p ≤ 0.05). Neither KT5720 nor KT5823 had any effect on ANP or CNP relaxant responses whereas gallein significantly inhibited both ANP (EC50 25.9 ± 0.09nM, p≤0.05) and CNP responses (EC50 93.9 ± 5.5nM, p ≤ 0.05), but had no effect on the vasodilator response of SNP (EC50 18 ± 5.3nM).

In conclusion, our data show that blockade of KV7 channels impairs relaxations of rat aorta generated by an NO-donor or natriuretic peptide receptor agonists. However, the mechanism by which KV7 channels are recruited appears to differ between the different agents. This suggests that KV7 channels may be differentially regulated in endogenous vasodilator responses by cGMP (SNP), or G-protein βγ subunits (ANP and CNP).

1. Chadha PS et al, Hypertension 59:877, 2012