38 research outputs found

    Mechanistic Insights into the Modulation of Voltage-Gated Ion Channels by Inhalational Anesthetics

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    AbstractGeneral anesthesia is a relatively safe medical procedure, which for nearly 170 years has allowed life saving surgical interventions in animals and people. However, the molecular mechanism of general anesthesia continues to be a matter of importance and debate. A favored hypothesis proposes that general anesthesia results from direct multisite interactions with multiple and diverse ion channels in the brain. Neurotransmitter-gated ion channels and two-pore K+ channels are key players in the mechanism of anesthesia; however, new studies have also implicated voltage-gated ion channels. Recent biophysical and structural studies of Na+ and K+ channels strongly suggest that halogenated inhalational general anesthetics interact with gates and pore regions of these ion channels to modulate function. Here, we review these studies and provide a perspective to stimulate further advances

    Exploring volatile general anesthetic binding to a closed membrane-bound bacterial voltage-gated sodium channel via computation.

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    Despite the clinical ubiquity of anesthesia, the molecular basis of anesthetic action is poorly understood. Amongst the many molecular targets proposed to contribute to anesthetic effects, the voltage gated sodium channels (VGSCs) should also be considered relevant, as they have been shown to be sensitive to all general anesthetics tested thus far. However, binding sites for VGSCs have not been identified. Moreover, the mechanism of inhibition is still largely unknown. The recently reported atomic structures of several members of the bacterial VGSC family offer the opportunity to shed light on the mechanism of action of anesthetics on these important ion channels. To this end, we have performed a molecular dynamics flooding simulation on a membrane-bound structural model of the archetypal bacterial VGSC, NaChBac in a closed pore conformation. This computation allowed us to identify binding sites and access pathways for the commonly used volatile general anesthetic, isoflurane. Three sites have been characterized with binding affinities in a physiologically relevant range. Interestingly, one of the most favorable sites is in the pore of the channel, suggesting that the binding sites of local and general anesthetics may overlap. Surprisingly, even though the activation gate of the channel is closed, and therefore the pore and the aqueous compartment at the intracellular side are disconnected, we observe binding of isoflurane in the central cavity. Several sampled association and dissociation events in the central cavity provide consistent support to the hypothesis that the fenestrations present in the membrane-embedded region of the channel act as the long-hypothesized hydrophobic drug access pathway

    Modulation of voltage-gated potassium and sodium channels by halogenated general anesthetics: Structural and biophysical insights into the mechanisms of action

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    General anesthesia results from complex interactions involving ion channels in the brain. Halogenated inhaled general anesthetics modulate voltage-gated ion channels, but the underlying molecular mechanisms are not understood. Inhaled anesthetics may act as positive and negative allosteric gating modifiers by interacting with critical hydrophobic pockets in the ion channel. A combination of scanning mutagenesis, electrophysiology, kinetic analysis and structural modeling was used to probe halogenated general anesthetic interactions with two model voltage-gated ion channels: K-Shaw2 (K +-selective) and NaChBac (Na+-selective). In K-Shaw2, the modulation is anesthetic-specific. Halothane, isoflurane and desflurane inhibit this ion channel, while sevoflurane, the more heavily fluorinated anesthetic, activates it. In NaChBac, sevoflurane alone produces overlapping responses with opposite effects. Whereas the response to low sevoflurane concentrations (0.2 mM) is dominated by activation, at high concentrations of sevoflurane (2 mM), there is additionally evidence for open-channel block. Mutagenesis and structural modeling revealed multiple binding and allosteric sites associated with the activation and inactivation gating regions of the ion channels. Furthermore, kinetic analysis suggests that inhaled anesthetic-dependent activation results from destabilizing pre-open activated states, stabilizing the open state and/or eliminating inactivation. In contrast, inhibition might result from stabilization of pre-open closed states, more favorable inactivation and open-channel block. The novel dual allosteric modulation of voltage-gated ion channels by closely related halogenated anesthetics offers new opportunities to study the structural basis of anesthetic specificity. Moreover, these findings will help determine the inhaled anesthetic pharmacophore necessary to design general anesthetics with improved therapeutic indices

    Circadian and feeding cues integrate to drive rhythms of physiology in Drosophila insulin-producing cells

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    Circadian clocks regulate much of behavior and physiology, but the mechanisms by which they do so remain poorly understood. While cyclic gene expression is thought to underlie metabolic rhythms, little is known about cycles in cellular physiology. We found that Drosophila insulin-producing cells (IPCs), which are located in the pars intercerebralis and lack an autonomous circadian clock, are functionally connected to the central circadian clock circuit via DN1 neurons. Insulin mediates circadian output by regulating the rhythmic expression of a metabolic gene (sxe2) in the fat body. Patch clamp electrophysiology reveals that IPCs display circadian clock-regulated daily rhythms in firing event frequency and bursting proportion under light:dark conditions. The activity of IPCs and the rhythmic expression of sxe2 are additionally regulated by feeding, as demonstrated by night feeding-induced changes in IPC firing characteristics and sxe2 levels in the fat body. These findings indicate circuit-level regulation of metabolism by clock cells in Drosophila and support a role for the pars intercerebralis in integrating circadian control of behavior and physiology
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