Voltage-activated Ion Channels Research Articles

Spatial interactions impact on Ca-driven synaptic plasticity: An ionic cable theory perspective

We extend our previous paper on deriving an approximate analytical solution of a nonlinear cable equation by including other ion channels in neurons and calcium dynamics based on reaction-diffusion dynamics that lead to a system of nonlinear cable equations. Here, excitable dendrite possesses clusters of voltage-activated ion channels that are discretely distributed as point sources or hotspots of transmembrane current along a continuous cable structure of fixed length. Single and/or trains of action potentials and spatially distributed synaptic inputs drive the depolarisation and activate sparsely distributed voltage-dependent calcium channels. This leads to calcium influx and diffusion in the cable. Here, time-dependent analytical solutions were obtained by applying a perturbation expansion of the non-dimensional voltage (Φ) and non-dimensional calcium (ΦCa) and then solving the resulting set of integral equations. We use this framework to gain insights into calcium-driven synaptic plasticity in dendrites. Many previous studies have traditionally focused on the local impact of calcium on whether the synapse's strength is increased (potentiated) or decreased (depressed). Only recently have studies focusing on heterosynaptic plasticity been gaining popularity, and here we ask the question of how a local plasticity rule is influenced by the spatially and temporally distributed synaptic inputs. Specifically, we focus on how synaptic inputs and calcium influx impact a calcium-derived temporal learning window for spike-timing-dependent plasticity (STDP) at nearby sites to assess the nature of the resulting distance-dependent interaction on the associated learning window at the synapse of interest.

The role of melatonin in regulating horticultural crop production under various abiotic stresses

Horticultural crops are very important component of our food chain, and their production is highly sensitive to different soil related abiotic stresses (SRAS). These stresses reduce plant growth and development by reducing seed germination (SG), seedling establishment, photosynthesis, reproduction, thus reduce fruit yield and quality. Nonetheless application of plant growth regulators has been shown a very promising technique to confer SRAS tolerance in horticultural crops. Melatonin (Mel)-a high conserved and stress regulatory molecule regulates a plethora of stress adaptive responses in plants. This paper summarizes the current state of knowledge of Mel involvement in regulating stress adaptive responses under SRAS. The major topic covered in this review included: (i) the effects of exogenous Mel application on seed germination, photosynthesis, flowering, and fruit yield under different SRAS, (ii) Mel crosstalk with stress regulatory mechanism to confer stress tolerance in horticultural crops. Latter topic further discussed the role of Mel in regulating (i) redox regulation, (ii) ionic homeostasis, and (iii) hormonal regulation. We show that Mel regulates stress adaptive responses and improves plant growth by allowing the direct scavenging of ROS, up-regulation of H+-ATPase activity and vacuolar sequestration of toxic ions in cytosol and activation of ROS-Ca2+ hub, which latter prevent the negative effects of ROS and membrane depolarization on the ROS-activated and voltage-activated ion channels. Such Mel mediated desensitization of ion channels may play a crucial role in reducing stress induced efflux of mineral ions such as K, Zn, Mg from cytosol, thereby improving plant growth. Moreover, Mel may operate in tandem with polyamines to regulate the biosynthesis of different phytohormones. However, studies are required to reveal the molecular identity of genes relating to Mel-polyamine tandem and to light signaling that could directly regulate phytohormone biosynthesis and the interaction of Mel with light signaling in regulating SG.

A brief exposure to toluene vapor alters the intrinsic excitability of D2 medium spiny neurons in the rat ventral striatum.

Although volatile organic solvents such as toluene are used for commercial and industrial uses, they are often voluntarily inhaled for their intoxicating and euphoric effects. Research into the effects of inhalants such as toluene on brain function have revealed actions on a variety of ligand-gated and voltage-activated ion channels involved in regulating neuronal excitability. Previous work from this laboratory has also shown that brief exposures to toluene vapor induce changes in the intrinsic excitability and synaptic transmission of neurons within the medial prefrontal cortex and ventral tegmental area that vary depending on projection target. In the present study, we recorded current-evoked spiking of medium spiny neurons (MSNs) in the nucleus accumbens (NAc) core and shell in adolescent rats exposed to an intoxicating concentration of toluene vapor. Compared to air controls, firing of NAc core MSNs in Sprague-Dawley rats was not altered 24 h after exposure to 10,500 ppm toluene vapor while spiking of NAc shell MSNs was enhanced at low current steps but reduced at higher current steps. When the rheobase current was used to putatively identify MSN subtypes, both "D1-like" and "D2-like" MSNs within the NAc shell but not core showed toluene-induced changes in firing. As toluene may itself have altered the rheobase resulting in misclassification of neuron subtype, we conducted additional studies using adolescent D2-Cre rats infused with a Cre-dependent mCherry reporter virus. Following toluene vapor exposure, spiking of NAc shell D2+ MSNs was enhanced at low current steps but inhibited at higher currents as compared to air controls while there were no differences in the firing of NAc shell D2- MSNs. The toluene-induced change in NAc D2+ shell MSN firing was accompanied by alterations in membrane resistance, rheobase, action potential rise time and height with no changes noted in D2- MSNs. Overall, these data add to a growing literature showing that brief exposures to intoxicating concentrations of toluene vapor causes selective alterations in the excitability of neurons within the addiction neurocircuitry that vary depending on sub-region, cell-type and projection target.

Characterization of mechanosensitive and voltage-activated ion channels in nociceptive Schwann cells.

Chronic pain is a pressing worldwide health problem, affecting nearly one fifth of the population. Our sense of pain has traditionally been thought of as arising entirely by the activation of nociceptive nerve endings in the skin, which are metabolically supported and protected by surrounding Schwann cells. However, it has recently been shown that a molecularly and morphologically unique Schwann cell subtype at the dermal-epidermal border of the skin exhibits mechanosensitive properties and may initiate mechanical pain. The ion channels expressed in these Schwann cells and their electrophysiological properties remain to be defined. In the present study, we isolated primary cutaneous Schwann cells expressing Tomato using the Sox10 promoter from hind paw mouse skin, maintained them in culture for 2-6 days, and used patch-clamp recordings to record macroscopic ionic currents. Mechanical stimulation of isolated cells at negative holding potentials evoked inward currents, confirming the expression of mechanosensitive ion channels. We also observed robust voltage-activated currents in nociceptive Schwann cells that only slowly inactivate, likely arising from voltage-activated potassium (Kv) channels in the Kv1 family. In some cells we also measured voltage-activated currents likely arising from a relatively non-selective cation channel. We are currently using genetic, pharmacological and biophysical approaches to define the molecular identity of mechanosensitive and voltage-activated ion channels expressed in nociceptive Schwann cells so their roles in sensing mechanical pain can be further explored.

Freeze-Frame Imaging of Dendritic Calcium Signals With TubuTag.

The extensive dendritic arbor of neurons is thought to be actively involved in the processing of information. Dendrites contain a rich diversity of ligand- and voltage-activated ion channels as well as metabotropic receptors. In addition, they are capable of releasing calcium from intracellular stores. Under specific conditions, large neurons produce calcium spikes that are locally restricted to a dendritic section. To investigate calcium signaling in dendrites, we introduce TubuTag, a genetically encoded ratiometric calcium sensor anchored to the cytoskeleton. TubuTag integrates cytoplasmic calcium signals by irreversible photoconversion from green to red fluorescence when illuminated with violet light. We used a custom two-photon microscope with a large field of view to image pyramidal neurons in CA1 at subcellular resolution. Photoconversion was strongest in the most distal parts of the apical dendrite, suggesting a gradient in the amplitude of dendritic calcium signals. As the read-out of fluorescence can be performed several hours after photoconversion, TubuTag will help investigating dendritic signal integration and calcium homeostasis in large populations of neurons.

Ion current and action potential alterations in peripheral neurons subject to uniaxial strain.

Peripheral nerves, subject to continuous elongation and compression during everyday movement, contain neuron fibers vital for movement and sensation. At supraphysiological strains resulting from trauma, chronic conditions, aberrant limb positioning, or surgery, conduction blocks occur which may result in chronic or temporary loss of function. Previous in vitro stretch models, mainly focused on traumatic brain injury modelling, have demonstrated altered electrophysiological behavior during localized deformation applied by pipette suction. Our aim was to evaluate the changes in voltage‐activated ion channel function during uniaxial straining of neurons applied by whole‐cell deformation, more physiologically relevant model of peripheral nerve trauma. Here, we quantified experimentally the changes in inwards and outwards ion currents and action potential (AP) firing in dorsal root ganglion‐derived neurons subject to uniaxial strains, using a custom‐built device allowing simultaneous cell deformation and patch clamp recording. Peak inwards sodium currents and rectifying potassium current magnitudes were found to decrease in cells under stretch, channel reversal potentials were found to be left‐shifted, and half‐maximum activation potentials right‐shifted. The threshold for AP firing was increased in stretched cells, although neurons retained the ability to fire induced APs. Overall, these results point to ion channels being damaged directly and immediately by uniaxial strain, affecting cell electrophysiological activity, and can help develop prevention and treatment strategies for peripheral neuropathies caused by mechanical trauma.

TMEM266 is a functional voltage sensor regulated by extracellular Zn2.

Voltage-activated ion channels contain S1-S4 domains that sense membrane voltage and control opening of ion-selective pores, a mechanism that is crucial for electrical signaling. Related S1-S4 domains have been identified in voltage-sensitive phosphatases and voltage-activated proton channels, both of which lack associated pore domains. hTMEM266 is a protein of unknown function that is predicted to contain an S1-S4 domain, along with partially structured cytoplasmic termini. Here we show that hTMEM266 forms oligomers, undergoes both rapid (µs) and slow (ms) structural rearrangements in response to changes in voltage, and contains a Zn2+ binding site that can regulate the slow conformational transition. Our results demonstrate that the S1-S4 domain in hTMEM266 is a functional voltage sensor, motivating future studies to identify cellular processes that may be regulated by the protein. The ability of hTMEM266 to respond to voltage on the µs timescale may be advantageous for designing new genetically encoded voltage indicators.

Context and Complexity: How Ionic Conductances Interact to Control Neuronal Firing

The action potential in the squid giant axon is generated by just two voltage-activated conductances, but mammalian neurons typically express well over a dozen different kinds of voltage-activated ion channels. Different types of neurons express different combinations of ion channels, with an especially high degree of diversity in the expression of potassium channels. How do particular combinations of ion channels interact to produce the variety of firing patterns seen in different kinds of neurons? This question can be addressed by a variety of experimental and computational approaches. Experimentally, the components of current flowing during action potentials can be “deconstructed” using the action potential clamp technique, in which a neuron is voltage clamped using its own trajectory of action potential firing as a command waveform and individual components of current are then defined by using selective pharmacological inhibitors. Two key lessons from analyzing how combinations of channels control firing patterns of mammalian neurons are: 1) Very small currents of 10's of pA flowing between spikes can powerfully influence spiking patterns. These currents often represent only a tiny open probability of the channel and may be hard to predict accurately by channel models formulated to fit much larger step-activated currents. 2) The influence of a particular channel type on firing can depend critically on the context of the other channels present. This is illustrated by several cases in which inhibiting particular voltage-dependent potassium channels has the paradoxical effect of slowing the rate of firing.

Single-particle cryo-EM structure of a voltage-activated potassium channel in lipid nanodiscs.

Voltage-activated potassium (Kv) channels open to conduct K+ ions in response to membrane depolarization, and subsequently enter non-conducting states through distinct mechanisms of inactivation. X-ray structures of detergent-solubilized Kv channels appear to have captured an open state even though a non-conducting C-type inactivated state would predominate in membranes in the absence of a transmembrane voltage. However, structures for a voltage-activated ion channel in a lipid bilayer environment have not yet been reported. Here we report the structure of the Kv1.2-2.1 paddle chimera channel reconstituted into lipid nanodiscs using single-particle cryo-electron microscopy. At a resolution of ~3 Å for the cytosolic domain and ~4 Å for the transmembrane domain, the structure determined in nanodiscs is similar to the previously determined X-ray structure. Our findings show that large differences in structure between detergent and lipid bilayer environments are unlikely, and enable us to propose possible structural mechanisms for C-type inactivation.

Deglycosylation of Shaker KV channels affects voltage sensing and the open-closed transition.

Most membrane proteins are subject to posttranslational glycosylation, which influences protein function, folding, solubility, stability, and trafficking. This modification has been proposed to protect proteins from proteolysis and modify protein-protein interactions. Voltage-activated ion channels are heavily glycosylated, which can result in up to 30% of the mature molecular mass being contributed by glycans. Normally, the functional consequences of glycosylation are assessed by comparing the function of fully glycosylated proteins with those in which glycosylation sites have been mutated or by expressing proteins in model cells lacking glycosylation enzymes. Here, we study the functional consequences of deglycosylation by PNGase F within the same population of voltage-activated potassium (KV) channels. We find that removal of sugar moieties has a small, but direct, influence on the voltage-sensing properties and final opening-closing transition of Shaker KV channels. Yet, we observe that the interactions of various ligands with different domains of the protein are not affected by deglycosylation. These results imply that the sugar mass attached to the voltage sensor neither represents a cargo for the dynamics of this domain nor imposes obstacles to the access of interacting molecules.

Voltage-Activated Ion Channels in Non-excitable Cells-A Viewpoint Regarding Their Physiological Justification.

Voltage-Activated Ion Channels in Non-excitable Cells-A Viewpoint Regarding Their Physiological Justification.

Interaction of a dinoflagellate neurotoxin with voltage-activated ion channels in a marine diatom.

BackgroundThe potent neurotoxins produced by the harmful algal bloom species Karenia brevis are activators of sodium voltage-gated channels (VGC) in animals, resulting in altered channel kinetics and membrane hyperexcitability. Recent biophysical and genomic evidence supports widespread presence of homologous sodium (Na+) and calcium (Ca2+) permeable VGCs in unicellular algae, including marine phytoplankton. We therefore hypothesized that VGCs of these phytoplankton may be an allelopathic target for waterborne neurotoxins produced by K. brevis blooms that could lead to ion channel dysfunction and disruption of signaling in a similar manner to animal Na+ VGCs.MethodsWe examined the interaction of brevetoxin-3 (PbTx-3), a K. brevis neurotoxin, with the Na+/Ca2+ VGC of the non-toxic diatom Odontella sinensis using electrophysiology. Single electrode current- and voltage- clamp recordings from O. sinensis in the presence of PbTx-3 were used to examine the toxin’s effect on voltage gated Na+/Ca2+ currents. In silico analysis was used to identify the putative PbTx binding site in the diatoms. We identified Na+/Ca2+ VCG homologs from the transcriptomes and genomes of 12 diatoms, including three transcripts from O. sinensis and aligned them with site-5 of Na+ VGCs, previously identified as the PbTx binding site in animals.ResultsUp to 1 µM PbTx had no effect on diatom resting membrane potential or membrane excitability. The kinetics of fast inward Na+/Ca2+ currents that underlie diatom action potentials were also unaffected. However, the peak inward current was inhibited by 33%, delayed outward current was inhibited by 25%, and reversal potential of the currents shifted positive, indicating a change in permeability of the underlying channels. Sequence analysis showed a lack of conservation of the PbTx binding site in diatom VGC homologs, many of which share molecular features more similar to single-domain bacterial Na+/Ca2+ VGCs than the 4-domain eukaryote channels.DiscussionAlthough membrane excitability and the kinetics of action potential currents were unaffected, the permeation of the channels underlying the diatom action potential was significantly altered in the presence of PbTx-3. However, at environmentally relevant concentrations the effects of PbTx- on diatom voltage activated currents and interference of cell signaling through this pathway may be limited. The relative insensitivity of phytoplankton VGCs may be due to divergence of site-5 (the putative PbTx binding site), and in some cases, such as O. sinensis, resistance to toxin effects may be because of evolutionary loss of the 4-domain eukaryote channel, while retaining a single domain bacterial-like VGC that can substitute in the generation of fast action potentials.

Reconstitution of Voltage-Activated Potassium Channel into Phospholipid Bilayer

Voltage-activated ion channels are expressed in the membranes of excitable cells, and open and close in response to changes in membrane voltage. Physiologically, they play diverse roles, from the generation of action potentials to triggering the release of neurotransmitters at synapses. To study the biochemical properties, these ion channels are usually purified and studied under detergent-solubilized condition, but many ion channels behave differently in detergent when compared to their native membrane environment. One recently introduced technique to overcome this issue is using lipid bilayer nanodiscs. Nanodiscs are a few nanometer-sized hockey-puck-shaped lipid bilayers solubilized by engineered apolipoprotein, membrane scaffold protein (MSP). MSP is comprised of short repeats of amphipathic alpha helies that surround the hydrophobic acyl chains of phospholipids. To investigate the structure and biochemical properties of voltage-activated potassium (Kv) channels in a membrane environment, we reconstituted a Kv channel into phospholipid bilayer nanodiscs using phospholipid and MSP. We first attempted to assemble empty nandiscs (nanodisc without Kv) to determine the optimal ratio between lipid and MSP that provides the best yields. Using these conditions, we reconstituted Kv channels into nanodiscs, and show that they elute as a single peak in gel-filtration chromatography. SDS-PAGE result indicates that the preparation contains each subunit corresponding to the Kv and MSP, confirming successful reconstitution of the Kv into nanodiscs. We also show that a voltage-sensor toxin can bind to the Kv channel in nanodiscs, confirming that the architecture of the Kv channel is well maintained in nanodiscs.

Inactivation of KCNQ1 potassium channels reveals dynamic coupling between voltage sensing and pore opening

In voltage-activated ion channels, voltage sensor (VSD) activation induces pore opening via VSD-pore coupling. Previous studies show that the pore in KCNQ1 channels opens when the VSD activates to both intermediate and fully activated states, resulting in the intermediate open (IO) and activated open (AO) states, respectively. It is also well known that accompanying KCNQ1 channel opening, the ionic current is suppressed by a rapid process called inactivation. Here we show that inactivation of KCNQ1 channels derives from the different mechanisms of the VSD-pore coupling that lead to the IO and AO states, respectively. When the VSD activates from the intermediate state to the activated state, the VSD-pore coupling has less efficacy in opening the pore, producing inactivation. These results indicate that different mechanisms, other than the canonical VSD-pore coupling, are at work in voltage-dependent ion channel activation.

Using Unnatural Amino Acids to Probe the Interaction between Tarantula Toxins and Voltage Sensing Domains in KV Channels

Peptide toxins folded into an inhibitor cystine knot (ICK) are found in the venoms of a variety of organisms (spider, scorpion, snakes, etc.), and many of these target the voltage-sensing domains in voltage-activated ion channels to modulate their gating properties. Our previous studies suggest that tarantula toxins partition into the lipid membrane and bind to the S3b-S4 paddle motif within the voltage-sensing domains to allosterically inhibit Kv channels. Alanine scanning mutagenesis studies have identified candidate residues in both toxin and channel that may contribute to forming the protein-protein interface when in complex. To definitively identify protein interaction surfaces between toxin and Kv channel, we employed unnatural amino acids and Strain - Promoted Azide Alkyne Click (SPAAC) chemistry to carry out site-specific crosslinking. Azidohomoalanine (AHA), an analog of methionine, was incorporated in Kv channels expressed in Xenopus laevis oocytes through endogenous methionyl t-RNA synthetase by supplementing excess of AHA in the medium. Simultaneously, guangxitoxin-1E (GxTx-1E) was engineered with spinster cysteine residues to incorporate an azide-reactive dibenzocyclooctyne (DBCO) group using cysteine-maleimide conjugation method. Currently, we are assaying for toxin-channel crosslinks in a functional manner by analyzing the recovery of macroscopic ionic currents and kinetics of toxin dissociation using two-electrode voltage clamp (TEVC) technique.

Characterization of a Fast Voltage-Sensing Protein using Voltage-Clamp Fluorometry

Voltage-sensing domains in voltage-activated ion channels and other voltage-sensing proteins contain well-conserved S4 helices containing basic residues capable of sensing changes in membrane potential to trigger opening or closing of ion-selective pores or phosphatase activity in voltage-sensitive phosphatases. Here we report the discovery of a protein which contains a voltage-sensing domain capable of rapid and slow rearrangements in response to changes in voltage. In place of a pore domain, this voltage sensor has large N- and C-termini predicted to contain structured and disordered domains for interaction with intracellular proteins. Our working hypothesis is that this protein, which we name Coupled Voltage Sensor (CVS), functions as a voltage sensor that couples to intracellular signaling pathways (as yet undefined). Our goal in the present experiments was to demonstrate that CVS undergoes voltage-dependent conformation changes and to characterize those using site-specific voltage-clamp fluorometry. We identified several positions at the external end of S4 where introduced and fluorophore-labeled Cys residues produce changes in fluorescence as a function of membrane potential. Several positions give complex fluorescence responses, starting with a rapid fluorescence increase (dequenching), followed by slower fluorescence decrease (quenching). Interestingly the rapid component is as fast as the clamp speed when using the cut-open voltage clamp technique (tau ∼ 200 μs). To exclude the possibility of Stark effect we examined the effects of a series of soluble quenchers and observed enhanced quenching with membrane depolarization, consistent with an outward movement of the S4 helix. Overall, our results support a model in which CVS undergoes two temporally distinct conformation rearrangements in response to membrane depolarization.

Tarantula toxins use common surfaces for interacting with Kv and ASIC ion channels.

Tarantula toxins that bind to voltage-sensing domains of voltage-activated ion channels are thought to partition into the membrane and bind to the channel within the bilayer. While no structures of a voltage-sensor toxin bound to a channel have been solved, a structural homolog, psalmotoxin (PcTx1), was recently crystalized in complex with the extracellular domain of an acid sensing ion channel (ASIC). In the present study we use spectroscopic, biophysical and computational approaches to compare membrane interaction properties and channel binding surfaces of PcTx1 with the voltage-sensor toxin guangxitoxin (GxTx-1E). Our results show that both types of tarantula toxins interact with membranes, but that voltage-sensor toxins partition deeper into the bilayer. In addition, our results suggest that tarantula toxins have evolved a similar concave surface for clamping onto α-helices that is effective in aqueous or lipidic physical environments.

Distribution and function of HCN channels in the apical dendritic tuft of neocortical pyramidal neurons.

The apical tuft is the most remote area of the dendritic tree of neocortical pyramidal neurons. Despite its distal location, the apical dendritic tuft of layer 5 pyramidal neurons receives substantial excitatory synaptic drive and actively processes corticocortical input during behavior. The properties of the voltage-activated ion channels that regulate synaptic integration in tuft dendrites have, however, not been thoroughly investigated. Here, we use electrophysiological and optical approaches to examine the subcellular distribution and function of hyperpolarization-activated cyclic nucleotide-gated nonselective cation (HCN) channels in rat layer 5B pyramidal neurons. Outside-out patch recordings demonstrated that the amplitude and properties of ensemble HCN channel activity were uniform in patches excised from distal apical dendritic trunk and tuft sites. Simultaneous apical dendritic tuft and trunk whole-cell current-clamp recordings revealed that the pharmacological blockade of HCN channels decreased voltage compartmentalization and enhanced the generation and spread of apical dendritic tuft and trunk regenerative activity. Furthermore, multisite two-photon glutamate uncaging demonstrated that HCN channels control the amplitude and duration of synaptically evoked regenerative activity in the distal apical dendritic tuft. In contrast, at proximal apical dendritic trunk and somatic recording sites, the blockade of HCN channels decreased excitability. Dynamic-clamp experiments revealed that these compartment-specific actions of HCN channels were heavily influenced by the local and distributed impact of the high density of HCN channels in the distal apical dendritic arbor. The properties and subcellular distribution pattern of HCN channels are therefore tuned to regulate the interaction between integration compartments in layer 5B pyramidal neurons.

Vibrotactile sensitivity threshold: nonlinear stochastic mechanotransduction model of the Pacinian Corpuscle.

Based on recent discoveries of stretch and voltage activated ion channels in the receptive area of the Pacinian Corpuscle (PC), this paper describes a two-stage mechanotransduction model of its near threshold Vibrotactile (VT) sensitivity valid over 10Hz to a few kHz. The model is based on the nonlinear and stochastic behavior of the ion channels represented as dependent charge sources loaded with membrane impedance. It simulates the neural response of the PC considering the morphological and statistical properties of the receptor potential and action potential with the help of an adaptive relaxation pulse frequency modulator. This model also simulates the plateaus and nonmonotonic saturation of spike rate characteristics. The stochastic simulation based on the addition of mechanical and neural noise describes that the VT Sensitivity Threshold (VTST) at higher frequencies is more noise dependent. Above 800Hz even a SNR = 150 improves the neurophysiological VTST more than 3dBμ. In that frequency range, an absence of the entrainment threshold and a lower sensitivity index near the absolute threshold make the upper bound of the psychophysical VTST more dependent on the experimental protocol and physical set-up. This model can be extended to simulate the neural response of a group of PCs.

Synchrony and the single neuron

In synaptic integration, timing is everything. A new study demonstrates that voltage-activated ion channels transform spatially distributed synaptic input into a coherent neuronal output by countering time delays in the dendritic tree.