A Novel Role for HNO in Local and Spreading Vasodilatation in Rat Mesenteric Resistance Arteries

Abstract

Nitric oxide-mediated vasodilatation has previously been attributed to the uncharged form of the molecule (NO ), but increasing evidence suggests that nitroxyl (HNO) may play a significant role in endothelium-dependent relaxation. The aim of this study was to investigate the mechanisms underlying HNO-mediated vasodilatation in phenylephrine pre-constricted pressurized (70 mmHg) mesenteric arteries, and on membrane currents in isolated smooth muscle cells using whole cell and perforated patch clamp recordings. Angeli's salt (AS: nitroxyl donor), evoked concentration-dependent vasodilatation that was insensitive to the NO scavengers carboxy-PTIO and hydroxocobalamin (HXC), but sensitive to either the HNO scavenger L-cysteine, K-channel blockers (4-AP and iberiotoxin), raised [K + ] o , or inhibition of soluble guanylyl cyclase (ODQ). AS-evoked smooth muscle hyperpolarization significantly augmented K V current in an ODQ sensitive manner, and also increased the BK Ca current. Importantly, 30 mM AS initiated conducted or spreading vasodilatation, and following blockade of endothelial K-channels (TRAM-34 and apamin), ACh was able to evoke similar L-cysteine-sensitive conducted dilatation. These data show that vasodilatation induced by HNO is mediated by both K V and BK Ca channels, and suggest a physiological role in vasodilatation through the vasculature.

Nitroxyl donors retain their depressor effects in hypertension

“…Moreover, not only do thiols discriminate between the different redox forms of NO but thiol supplementation may augment the blood pressure lowering action of NO˙donors. Furthermore, to our previous demonstration that HNO donors are potent vasorelaxants (7,10,11,34) and resistant to the development of tolerance (11,12), this study highlights the potential for HNO donors as effective antihypertensive agents. These findings support the growing body of evidence that HNO donors may offer a therapeutic alternative to traditional nitrovasodilators (4,19,23,24) in the treatment of cardiovascular disorders.…”

“…Although NAC can interact with a number of signaling molecules to influence the cellular redox milieu, its ability to increase MAP may also suggest that putative endogenous HNO is generated in pathophysiological conditions. Given HNO has recently been shown to serve as an endothelium-derived relaxing factor in the resistance vasculature (1,34) and biochemical studies have suggested that HNO can be derived from uncoupled NO synthase (NOS) and following oxidation of the NOS intermediates N-hydroxy-L-arginine and hydroxylamine (13), then an augmented endogenous production in the setting of disease could be anticipated. However, it is important to note that although NAC did not alter basal MAP in normotensive WKY rats, we have previously reported a significant increase in MAP in response to NAC in a different cohort of WKY rats (12).…”

“…Indeed HNO serves as a potent vasodilator both in vitro (1,5,(7)(8)(9)(10)(11)34) and in vivo (12,19,23,24). HNO donors such as Angeli's salt (AS; sodium trioxodinitrate) and isopropylamine NONOate (IPA/NO) exhibit vasorelaxant activity in both large isolated conduit (5,8,11) and small resistance (1,10) arteries.…”

“…Such effects, like NO˙, are mediated predominantly via activation of soluble guanylyl cyclase (sGC) (10,11) and the resulting accumulation of cGMP (8,11). However, in contrast with NO˙, HNO can also target distinct vascular signaling pathways including voltage-gated K ϩ (K v ) channels (1,7,10,34), ATP-sensitive K ϩ channels (K ATP ) (7), and calcitonin gene-related peptide (CGRP) release (7).…”

Soluble Guanylate Cyclase Is Required for Systemic Vasodilation But Not Positive Inotropy Induced by Nitroxyl in the Mouse

“…-like activity on soluble guanylate cyclase (sGC) triggering cGMP-dependent signaling, activation of voltage and calcium-dependent potassium hyperpolarizing channels 3, 6 , and the stimulation of calcitonin gene related peptide (CGRP) 18 . HNO-vasodilation is blocked in vitro by the sGC antagonist [1H-[1,2,4]oxadiazolo-[4, 3-a]quinoxalin-1-one] (ODQ) 4-6, 19, 20 , which has been interpreted as supporting an sGC dependent mechanism. However, whether HNO directly interacts with sGC heme has been questioned by molecular model analysis 21 and data showing this requires HNO conversion to NO .…”