Explore the vast range of titles available.

The term endothelium-derived hyperpolarising factor (EDHF) was introduced in 1987 to describe the hypothetical factor responsible for myocyte hyperpolarisations not associated with nitric oxide (EDRF) or prostacyclin. Two broad categories of EDHF response exist. The classical EDHF pathway is blocked by apamin plus TRAM-34 but not by apamin plus iberiotoxin and is associated with endothelial cell hyperpolarisation. This follows an increase in intracellular [Ca 2+ ] and the opening of endothelial SK Ca and IK Ca channels preferentially located in caveolae and in endothelial cell projections through the internal elastic lamina, respectively. In some vessels, endothelial hyperpolarisations are transmitted to myocytes through myoendothelial gap junctions without involving any EDHF. In others, the K + that effluxes through SK Ca activates myocytic and endothelial Ba 2+ -sensitive K IR channels leading to myocyte hyperpolarisation. K + effluxing through IK Ca activates ouabain-sensitive Na + /K + -ATPases generating further myocyte hyperpolarisation. For the classical pathway, the hyperpolarising “factor” involved is the K + that effluxes through endothelial K Ca channels. During vessel contraction, K + efflux through activated myocyte BK Ca channels generates intravascular K + clouds. These compromise activation of Na + /K + -ATPases and K IR channels by endothelium-derived K + and increase the importance of gap junctional electrical coupling in myocyte hyperpolarisations. The second category of EDHF pathway does not require endothelial hyperpolarisation. It involves the endothelial release of factors that include NO, HNO, H 2 O 2 and vasoactive peptides as well as prostacyclin and epoxyeicosatrienoic acids. These hyperpolarise myocytes by opening various populations of myocyte potassium channels, but predominantly BK Ca and/or K ATP , which are sensitive to blockade by iberiotoxin or glibenclamide, respectively.

Despite numerous reports implicating salicylic acid (SA) in plant salinity responses, the specific ionic mechanisms of SA-mediated adaptation to salt stress remain elusive. To address this issue, a non-invasive microelectrode ion flux estimation technique was used to study kinetics of NaCl-induced net ion fluxes in Arabidopsis thaliana in response to various SA concentrations and incubation times. NaCl-induced K+ efflux and H+ influx from the mature root zone were both significantly decreased in roots pretreated with 10–500 μM SA, with strongest effect being observed in the 10–50 μM SA range. Considering temporal dynamics (0–8-h SA pretreatment), the 1-h pretreatment was most effective in enhancing K+ retention in the cytosol. The pharmacological, membrane potential, and shoot K+ and Na+ accumulation data were all consistent with the model in which the SA pretreatment enhanced activity of H+-ATPase, decreased NaCl-induced membrane depolarization, and minimized NaCl-induced K+ leakage from the cell within the first hour of salt stress. In long-term treatments, SA increased shoot K+ and decreased shoot Na+ accumulation. The short-term NaCl-induced K+ efflux was smallest in the gork1-1 mutant, followed by the rbohD mutant, and was highest in the wild type. Most significantly, the SA pretreatment decreased the NaCl-induced K+ efflux from rbohD and the wild type to the level of gork1-1, whereas no effect was observed in gork1-1. These data provide the first direct evidence that the SA pretreatment ameliorates salinity stress by counteracting NaCl-induced membrane depolarization and by decreasing K+ efflux via GORK channels.

K + channels are important regulators of arterial tone by providing membrane hyperpolarization and thus counteracting the activity of voltage-gated Ca 2+ channels in the smooth muscle and, thus, vasoconstriction. The endothelium and smooth muscle express a variety of different K + channels, such as Ca 2+ -activated K + channels (KCa), voltage-gated (KV), two-pore-domain (K2P), and inward rectifying (KIR) and KATP channels. Their contributions to the numerous mechanisms of endothelium-dependent and smooth muscle-dependent relaxation are closely related to their electrophysiological properties, activation mechanisms, and to differential expressions pattern within the vascular wall. Here, we summarize the cardiovascular phenotypes in murine models of genetic K + -channel deficiency and focus, in particular, on defective vasoregulation in mice deficient of endothelial Ca 2+ -activated K + channels, IK (KCa3.1) and SK (KCa2.3), and smooth muscle Ca 2+ -activated K + channels, BK (KCa.1.1). Genetic deficiency of endothelial IK and SK severely impairs the endothelium-derived hyperpolarization-mediated type of arterial dilation. Moreover, SK deficiency impairs NO-mediated dilator responses, thus indicating subtype-specific actions in endothelial function. Loss of IK and/or SK channels is associated with sizeable higher blood pressure. In contrast, genetic deficiency of smooth BK channels enhances arterial blood pressure which is linked to mainly a loss of spontaneous transient outward currents in the smooth muscle cells as well as renal and adrenal gland functions (hyperaldosteronism). In conclusion, genetic deficiency of vascular K + channels results in severe impairments of local and systemic blood pressure regulation. These alterations strengthen the perspective that vascular K + channels are potential pharmacologic targets for improvement of vasodilator functions in cardiovascular pathologies.

Longden et al . demonstrate that brain capillaries function as a vast sensory web, monitoring neuronal activity by sensing K + and translating this into a K IR -channel-mediated regenerative retrograde hyperpolarizing signal that propagates to upstream arterioles to drive vasodilation and an increase in blood flow into the capillary bed. Blood flow into the brain is dynamically regulated to satisfy the changing metabolic requirements of neurons, but how this is accomplished has remained unclear. Here we demonstrate a central role for capillary endothelial cells in sensing neural activity and communicating it to upstream arterioles in the form of an electrical vasodilatory signal. We further demonstrate that this signal is initiated by extracellular K + —a byproduct of neural activity—which activates capillary endothelial cell inward-rectifier K + (K IR 2.1) channels to produce a rapidly propagating retrograde hyperpolarization that causes upstream arteriolar dilation, increasing blood flow into the capillary bed. Our results establish brain capillaries as an active sensory web that converts changes in external K + into rapid, 'inside-out' electrical signaling to direct blood flow to active brain regions.

It is becoming increasingly evident that electrical signaling via gap junctions plays a central role in the physiological control of vascular tone via two related mechanisms (1) the endothelium-derived hyperpolarizing factor (EDHF) phenomenon, in which radial transmission of hyperpolarization from the endothelium to subjacent smooth muscle promotes relaxation, and (2) responses that propagate longitudinally, in which electrical signaling within the intimal and medial layers of the arteriolar wall orchestrates mechanical behavior over biologically large distances. In the EDHF phenomenon, the transmitted endothelial hyperpolarization is initiated by the activation of Ca 2+ -activated K + channels channels by InsP 3 -induced Ca 2+ release from the endoplasmic reticulum and/or store-operated Ca 2+ entry triggered by the depletion of such stores. Pharmacological inhibitors of direct cell-cell coupling may thus attenuate EDHF-type smooth muscle hyperpolarizations and relaxations, confirming the participation of electrotonic signaling via myoendothelial and homocellular smooth muscle gap junctions. In contrast to isolated vessels, surprisingly little experimental evidence argues in favor of myoendothelial coupling acting as the EDHF mechanism in arterioles in vivo. However, it now seems established that the endothelium plays the leading role in the spatial propagation of arteriolar responses and that these involve poorly understood regenerative mechanisms. The present review will focus on the complex interactions between the diverse cellular signaling mechanisms that contribute to these phenomena.

The transmembrane voltage gradient is a general physico-chemical cue that regulates diverse biological function through voltage-gated ion channels. How voltage sensing mediates ion flows remains unknown at the molecular level. Here, we report six conformations of the human Eag2 (hEag2) ranging from closed, pre-open, open, and pore dilation but non-conducting states captured by cryo-electron microscopy (cryo-EM). These multiple states illuminate dynamics of the selectivity filter and ion permeation pathway with delayed rectifier properties and Cole-Moore effect at the atomic level. Mechanistically, a short S4-S5 linker is coupled with the constrict sites to mediate voltage transducing in a non-domain-swapped configuration, resulting transitions for constrict sites of F464 and Q472 from gating to open state stabilizing for voltage energy transduction. Meanwhile, an additional potassium ion occupied at positions S6 confers the delayed rectifier property and Cole-Moore effects. These results provide insight into voltage transducing and potassium current across membrane, and shed light on the long-sought Cole-Moore effects. Human Eag2 is a voltage-gated potassium channel with unique delayed rectifying gating kinetics. Here, authors show how voltage opens the channel and illuminate a mechanism of delayed rectifier gating.

Potassium (K) channels exhibit exquisite selectivity for conduction of K + ions over other cations, particularly Na + . High-resolution structures reveal an archetypal selectivity filter (SF) conformation in which dehydrated K + ions, but not Na + ions, are perfectly coordinated. Using single-molecule FRET (smFRET), we show that the SF-forming loop (SF-loop) in KirBac1.1 transitions between constrained and dilated conformations as a function of ion concentration. The constrained conformation, essential for selective K + permeability, is stabilized by K + but not Na + ions. Mutations that render channels nonselective result in dilated and dynamically unstable conformations, independent of the permeant ion. Further, while wild-type KirBac1.1 channels are K + selective in physiological conditions, Na + permeates in the absence of K + . Moreover, whereas K + gradients preferentially support 86 Rb + fluxes, Na + gradients preferentially support 22 Na + fluxes. This suggests differential ion selectivity in constrained versus dilated states, potentially providing a structural basis for this anomalous mole fraction effect. Single-molecule FRET shows that a loop, which forms the selectivity filter in the bacterial inwardly rectifying K + channel KirBac1.1, transitions between constrained and dilated conformations depending on ion occupancy of the filter.

Intracellular Ca 2+ signals underlying conducted vasoconstriction to local application of a brief depolarizing KCl stimulus was investigated in rat mesenteric terminal arterioles (<40 μm). Using a computer model of an arteriole segment comprised of coupled endothelial cells (EC) and vascular smooth muscle cells (VSMC) simulations of both membrane potential and intracellular [Ca 2+ ] were performed. The “characteristic” length constant, λ , was approximated using a modified cable equation in both experiments and simulations. We hypothesized that K + conductance in the arteriolar wall limit the electrotonic spread of a local depolarization along arterioles by current dissipation across the VSMC plasma membrane. Thus, we anticipated an increased λ by inhibition of voltage-activated K + channels. Application of the BK Ca channel blocker iberiotoxin (100 nM) onto mesenteric arterioles in vitro and inhibition of BK Ca channel current in silico increased λ by 34% and 32%, respectively. Similarly, inhibition of K V channels in vitro (4-aminopyridine, 1 mM) or in silico increased λ by 41% and 21%, respectively. Immunofluorescence microscopy demonstrated expression of BK Ca , Kv1.5, Kv2.1, but not Kv1.2, in VSMCs of rat mesenteric terminal arterioles. Our results demonstrate that inhibition of voltage-activated K + channels enhance vascular-conducted responses to local depolarization in terminal arterioles by increasing the membrane resistance of VSMCs. These data contribute to our understanding of how differential expression patterns of voltage-activated K + channels may influence conducted vasoconstriction in small arteriolar networks. This finding is potentially relevant to understanding the compromised microcirculatory blood flow in systemic vascular diseases such as diabetes mellitus and hypertension.

Potassium channels form physical complexes with solute transporters in vivo, yet little is known about their range of possible signaling modalities and the underlying mechanisms. The KCNQ2/3 potassium channel, which generates neuronal M-current, is voltage-gated and its activity is also stimulated by binding of various small molecules. KCNQ2/3 forms reciprocally regulating complexes with sodium-coupled myo -inositol transporters (SMITs) in mammalian neurons. Here, we report that the neurotransmitter γ-aminobutyric acid (GABA) and other small molecules directly regulate myo -inositol transport in rat dorsal root ganglia, and by human SMIT1-KCNQ2/3 complexes in vitro, by inducing a distinct KCNQ2/3 pore conformation. Reciprocally, SMIT1 tunes KCNQ2/3 sensing of GABA and related metabolites. Ion permeation and mutagenesis studies suggest that SMIT1 and GABA similarly alter KCNQ2/3 pore conformation but via different KCNQ subunits and molecular mechanisms. KCNQ channels therefore act as chemosensors to enable co-assembled myo -inositol transporters to respond to diverse stimuli including neurotransmitters, metabolites and drugs. Manville and Abbott propose that KCNQ-subfamily potassium channels act as chemosensors to enable coassembled transporters to respond to diverse stimuli. They show that GABA and other small molecules directly regulate myo-inositol transport by inducing a distinct KCNQ2/3 pore conformation, while myo-inositol transporters (SMITs) tune KCNQ2/3 sensing of GABA and related metabolites.

Voltage-gated potassium channels KCNQ2–5 generate the M-current, which controls neuronal excitability. KCNQ2–5 subunits each harbor a high-affinity anticonvulsant drug-binding pocket containing an essential tryptophan (W265 in human KCNQ3) conserved for >500 million years, yet lacking a known physiological function. Here, phylogenetic analysis, electrostatic potential mapping, in silico docking, electrophysiology, and radioligand binding assays reveal that the anticonvulsant binding pocket evolved to accommodate endogenous neurotransmitters including γ-aminobutyric acid (GABA), which directly activates KCNQ5 and KCNQ3 via W265. GABA, and endogenous metabolites β-hydroxybutyric acid (BHB) and γ-amino-β-hydroxybutyric acid (GABOB), competitively and differentially shift the voltage dependence of KCNQ3 activation. Our results uncover a novel paradigm: direct neurotransmitter activation of voltage-gated ion channels, enabling chemosensing of the neurotransmitter/metabolite landscape to regulate channel activity and cellular excitability. M-current is conveyed by voltage-sensitive KCNQ channels, which are enriched in GABAergic neurons and are activated by anticonvulsants such as retigabine. Here the authors show that GABA directly activates KCNQ3, at the residue required for its anticonvulsant activity.