Abstract
The voltage-gated K+ channel has key roles in the vasculature and in atrial excitability and contributes to apoptosis in various tissues. In this study, we have explored its regulation by carbon monoxide (CO), a product of the cytoprotective heme oxygenase enzymes, and a recognized toxin. CO inhibited recombinant Kv1.5 expressed in HEK293 cells in a concentration-dependent manner that involved multiple signalling pathways. CO inhibition was partially reversed by superoxide dismutase mimetics and by suppression of mitochondrial reactive oxygen species. CO also elevated intracellular nitric oxide (NO) levels. Prevention of NO formation also partially reversed CO inhibition of Kv1.5, as did inhibition of soluble guanylyl cyclase. CO also elevated intracellular peroxynitrite levels, and a peroxynitrite scavenger markedly attenuated the ability of CO to inhibit Kv1.5. CO caused nitrosylation of Kv1.5, an effect that was also observed in C331A and C346A mutant forms of the channel, which had previously been suggested as nitrosylation sites within Kv1.5. Augmentation of Kv1.5 via exposure to hydrogen peroxide was fully reversed by CO. Native Kv1.5 recorded in HL-1 murine atrial cells was also inhibited by CO. Action potentials recorded in HL-1 cells were increased in amplitude and duration by CO, an effect mimicked and occluded by pharmacological inhibition of Kv1.5. Our data indicate that Kv1.5 is a target for modulation by CO via multiple mechanisms. This regulation has important implications for diverse cellular functions, including excitability, contractility and apoptosis.
Highlights
Kv1.5 is a rapidly activating, voltage-gated K+ channel encoded by KCNA5 that inactivates slowly and incompletely.[1]
As exemplified in the time-series plot of Figure 1a, CO-releasing molecules (CORMs)-2 caused a reversible inhibition of K+ current amplitudes, and this was associated with a marked slowing of activation kinetics (Figure 1c)
The present study demonstrates that both native and recombinant hKv1.5 K+ channels are inhibited by carbon monoxide (CO)
Summary
Kv1.5 is a rapidly activating, voltage-gated K+ channel encoded by KCNA5 that inactivates slowly and incompletely.[1]. Its expression/activity is associated with increased apoptosis in endothelial and smooth muscle cells.[5,6] In vascular smooth muscle cells (VSMCs) of the pulmonary vasculature, it is of particular importance to hypoxic pulmonary vasoconstriction[7,8,9] and in the development of pulmonary arterial hypertension (PAH).[10,11,12] Kv1.5 expression is reduced in PAH patients[13] and patients with idiopathic PAH possess important single-nucleotide polymorphisms in KCNA5, which encodes Kv1.5.14,15 In the systemic circulation, Kv1.5 contributes to repolarization of the VSMC membrane potential, limiting Ca2+ entry and vascular tone.[16,17,18] A recent study employing Kv1.5− / − mice has shown that this channel is essential for balancing coronary blood flow with metabolic demands of the working myocardium.[19]. Tonic ROS production by mitochondria or NADPH oxidase (Nox 4) sustains Kv1.5 activity and keeps pulmonary VSMCs relatively hyperpolarized.[31,32] In the coronary circulation, hydrogen peroxide (H2O2) has been proposed as the signal closely coupling cardiac metabolism to coronary blood flow[33,34,35] and this coupling appears via H2O2-mediated augmentation of Kv1.5.19 Recombinant Kv1.5 activity has been demonstrated to be directly augmented by H2O2.36
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