Vascular KATP channel structural dynamics reveal regulatory mechanism by Mg-nucleotides.

Vascular tone is dependent on smooth muscle KATP channels comprising pore-forming Kir6.1 and regulatory SUR2B subunits, in which mutations cause Cantú syndrome. Unique among KATP isoforms, they lack spontaneous activity and require Mg-nucleotides for activation. Structural mechanisms underlying these properties are unknown. Here, we determined cryogenic electron microscopy structures of vascular KATP channels bound to inhibitory ATP and glibenclamide, which differ informatively from similarly determined pancreatic KATP channel isoform (Kir6.2/SUR1). Unlike SUR1, SUR2B subunits adopt distinct rotational "propeller" and "quatrefoil" geometries surrounding their Kir6.1 core. The glutamate/aspartate-rich linker connecting the two halves of the SUR-ABC core is observed in a quatrefoil-like conformation. Molecular dynamics simulations reveal MgADP-dependent dynamic tripartite interactions between this linker, SUR2B, and Kir6.1. The structures captured implicate a progression of intermediate states between MgADP-free inactivated, and MgADP-bound activated conformations wherein the glutamate/aspartate-rich linker participates as mobile autoinhibitory domain, suggesting a conformational pathway toward KATP channel activation.

Effect of tobacco smoke on hydrogen sulfide-induced rat thoracic aorta relaxation

Levels of hydrogen sulfide (H2S), a gaseous signaling molecule, are reduced in the serum of individuals who smoke. We hypothesized that tobacco smoke influenced smooth muscle relaxation by decreasing H2S levels and this effect could also influence expression of cystathionine γ-lyase (CSE) and sulfonylurea receptor-2 (SUR-2). The aim of this study was to explore the effect of tobacco smoke on H2S-mediated rat thoracic aorta relaxation and its possible mechanism. Thirty-two Sprague-Dawley rats were divided into four groups: control (C) group, short-term smoker (SS) group, mid-term smoker (MS) group, and long-term smoker (LS) group. H2S concentrations in serum, action of H2S on rat aortic vascular relaxation, and expression of CSE and SUR-2 in thoracic aortic smooth muscle were measured. Although there was no significant difference in H2S between the C and the SS groups, concentration of H2S was significantly reduced in both the LS and MS groups compared to control (P<0.01). Furthermore, H2S was significantly lower in the LS than in the MS group (P<0.05). Rat aortic vascular relaxation was lower in all three treatment groups compared to the control, with the most significant decrease observed in the LS group (P<0.05 compared to the MS group). Expression of CSE and SUR-2 was reduced in the LS and MS groups compared to control (P<0.05), with the lowest levels observed in the LS group (P<0.05). Therefore, tobacco smoke reduced expression of CSE and SUR-2 in rat thoracic aorta, which may inhibit H2S production and vascular dilation.

Role of hydrogen sulfide in secondary neuronal injury.

In acute neuronal insult events, such as stroke, traumatic brain injury, and spinal cord injury, pathological processes of secondary neuronal injury play a key role in the severity of insult and clinical prognosis. Along with nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H2S) is regarded as the third gasotransmitter and endogenous neuromodulator and plays multiple roles in the central nervous system under physiological and pathological states, especially in secondary neuronal injury. The endogenous level of H2S in the brain is significantly higher than that in peripheral tissues, and is mainly formed by cystathionine ß-synthase (CBS) in astrocytes and released in response to neuronal excitation. The mechanism of secondary neuronal injury exacerbating the damage caused by the initial insult includes microcirculation failure, glutamate-mediated excitotoxicity, oxidative stress, inflammatory responses, neuronal apoptosis and calcium overload. H2S dilates cerebral vessels by activating smooth muscle cell plasma membrane ATP-sensitive K channels (KATP channels). This modification occurs on specific cysteine residues of the KATP channel proteins which are S-sulfhydrated. H2S counteracts glutamate-mediated excitotoxicity by inducing astrocytes to intake more glutamate from the extracellular space and thus increasing glutathione in neurons. In addition, H2S protects neurons from secondary neuronal injury by functioning as an anti-oxidant, anti-inflammatory and anti-apoptotic mediator. However, there are still some reports suggest that H2S elevates neuronal Ca(2+) concentration and may contribute to the formation of calcium overload in secondary neuronal injury. H2S also elicits calcium waves in primary cultures of astrocytes and may mediate signals between neurons and glia. Consequently, further exploration of the molecular mechanisms of H2S in secondary neuronal injury will provide important insights into its potential therapeutic uses for the treatment of acute neuronal insult events.