A hybrid approach to measuring electrical activity in genetically specified neurons

Chanda, Baron; Blunck, Rikard; Faria, Leonardo Coutinho; Schweizer, Felix E.; Módy, István; Bezanilla, Francisco

doi:10.1038/nn1558

Cited by 166 publications

(202 citation statements)

References 30 publications

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“…5A). Hybrid voltage sensors exploit this property to report voltage changes with fluorescence intensity (33). Because the degree and the halfvoltage of donor quenching are expected to depend on the axial distance of the donor from the membrane, and on FRET R 0 , we reasoned that the voltage dependence of fluorescence would pinpoint the positions of the insertion sites relative to the membrane.…”

Section: Voltage-dependent Quenching Of Yfp In the Intracellular Regimentioning

confidence: 99%

Structural rearrangement of the intracellular domains during AMPA receptor activation

Zachariassen

Katchan

Jensen

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are ligand-gated ion channels that mediate the majority of fast excitatory neurotransmission in the central nervous system. Despite recent advances in structural studies of AMPARs, information about the specific conformational changes that underlie receptor function is lacking. Here, we used single and dual insertion of GFP variants at various positions in AMPAR subunits to enable measurements of conformational changes using fluorescence resonance energy transfer (FRET) in live cells. We produced dual CFP/ YFP-tagged GluA2 subunit constructs that had normal activity and displayed intrareceptor FRET. We used fluorescence lifetime imaging microscopy (FLIM) in live HEK293 cells to determine distinct steady-state FRET efficiencies in the presence of different ligands, suggesting a dynamic picture of the resting state. Patch-clamp fluorometry of the double-and single-insert constructs showed that both the intracellular C-terminal domain (CTD) and the loop region between the M1 and M2 helices move during activation and the CTD is detached from the membrane. Our time-resolved measurements revealed unexpectedly complex fluorescence changes within these intracellular domains, providing clues as to how posttranslational modifications and receptor function interact.T he α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type ionotropic glutamate receptors (iGluRs) reside in postsynaptic membranes in the central nervous system (1). Like the other major iGluR subtypes, the N-methyl-Daspartate receptors (NMDARs) and kainate receptors, AMPARs are ligand-gated cation channels formed by hetero-or homotetrameric assembly of the GluA1 to GluA4 subunits into a membranespanning receptor with an integral ion channel. The energy from binding of the excitatory neurotransmitter glutamate at extracellular sites triggers AMPARs to passage through functional states that can include ion channel activation, deactivation, and desensitization. The timing and interplay between the necessarily distinct conformations of these states determine both basal transmission and short-term plasticity of the postsynapse (2-4).Structures of AMPARs captured in various functional states using X-ray crystallography and cryoelectron microscopy have recently become available (5-9). Overall, the structures confirm three distinct structural layers (Fig. 1). The amino-terminal domain (ATD) and the ligand-binding domain (LBD), both distal to the membrane, and the transmembrane ion channel are each formed from four copies of the respective domain from each subunit. However, a fourth region of the receptor extends from the intracellular side of the membrane. This part of the receptor includes intracellular loops between the transmembrane helices and the variable C-terminal domain (CTD), and remains entirely unresolved in the presently available AMPAR structures.The GluA2 structures and previous results from biochemical, biophysical, and crystallographic studies of isolated subunits and fu...

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Section: Voltage-dependent Quenching Of Yfp In the Intracellular Regimentioning

confidence: 99%

Structural rearrangement of the intracellular domains during AMPA receptor activation

Zachariassen

Katchan

Jensen

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Although FlaSh has been modified and improved for signal detection in mammalian systems, it has not been widely adopted [14]. Hybrid approaches that combined a membrane-bound GFP-sensor with a chemical fluorophore have yielded larger fractional fluorescence changes (up to 35% per 100 mV), but require delivery of exogenous and toxic dyes to the imaged cells [15]. Recently, a fluorescent voltage sensor derived from a non-ion channel phosphatase protein has been developed that shows good membrane targeting in mammalian cells, and as much as an 8% change/100 mV in fluorescence at physiological temperatures; however, it remains too slow to follow individual action potentials [16].…”

Section: Channel-based Voltage Sensorsmentioning

confidence: 99%

Visualizing circuits and systems using transgenic reporters of neural activity

Barth

2007

Current Opinion in Neurobiology

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Genetically encoded sensors of neural activity enable visualization of circuit-level function in the central nervous system. Although our understanding of the molecular events that regulate neuronal firing, synaptic function, and plasticity has expanded rapidly over the past fifteen years, an appreciation for how cellular changes are functionally integrated at the circuit level has lagged. A new generation of tools that employ fluorescent sensors of neural activity promises unique opportunities to bridge the gap between cellular and system-levels analysis.This review will focus on genetically-encoded sensors. A primary advantage of these indicators is that they can be non-selectively introduced to large populations of cells using either transgenic or viral-mediated approaches. This ability removes the non-trivial obstacles of how to get chemical indicators into cells of interest, a problem that has dogged investigators who have been interested in mapping neural function in the intact CNS. Five different types of approaches and their relative utility will be reviewed here: 1) reporters of immediate-early gene (IEG) activation using promoters such as c-fos and arc, 2) voltage-based sensors, such as GFPcoupled Na + and K + channels, 3) Cl − based sensors, 4) Ca ++ -based sensors, such as Camgaroo and the troponin-based TN-L15, and 5) pH-based sensors, which have been particularly useful for examining synaptic activity of highly convergent afferents in sensory systems in vivo. Particular attention will be paid to reporters of IEG expression, since these tools employ the built-in threshold function that occurs with activation of gene expression, provoking new experimental questions by expanding the timescale of analysis for circuit and system-level functional mapping. Fluorescent reporters of inducible gene expressionImmediate-early gene expression (IEG) can be a reliable marker of elevated neuronal firing, reporting activity over time scales that range from minutes to hours compared to ms and seconds for voltage-or ion-based sensors. In ion-based approaches, indicators are constitutively present in the cell, and the fluorescent protein must be engineered to be a sensor with rapid onset and offset kinetics to achieve temporal fidelity with the process being measured. In contrast, monitoring IEG expression can be directly coupled to transcription of the reporter gene. However, because maturation of the fluorophore is required for detection, a temporal delay may be introduced into reporter detection. This delay in reporting activity is advantageous in that it expands the types of experimental questions that can be addressed. For example, do IEGexpressing cells remain more excitable after stimulus cessation? Are cells activated by two temporally distinct stimuli (i.e. training and recall in a memory task) overlapping or distinct?

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“…[3][4][5][6][7][8] Nevertheless, though a useful correlation often exists between Ca 2+ dynamics and neuronal spiking across a range of spike frequencies, the slowkinetics and saturation of [Ca 2+ ]-related fluorescent signals constrain the utility of Ca 2+ imaging as a means of probing spiking dynamics in many neuron types. 4,9 Numerous voltage-sensitive indicators 1,[10][11][12][13][14][15][16][17][18] permit direct imaging of cellular membrane potentials. Organic voltage-sensitive dyes have allowed functional mapping studies in awake mammals 14 and studies of individual cells' dynamics in invertebrates 19 and mammalian brain slices.…”

Section: Introductionmentioning

confidence: 99%

Optical Strategies for Sensing Neuronal Voltage Using Quantum Dots and Other Semiconductor Nanocrystals

Marshall

Schnitzer

2013

ACS Nano

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Biophysicists have long sought optical methods capable of reporting the electrophysiological dynamics of large-scale neural networks with millisecond-scale temporal resolution. Existing fluorescent sensors of cell membrane voltage can report action potentials in individual cultured neurons, but limitations in brightness and dynamic range of both synthetic organic and genetically encoded voltage sensors have prevented concurrent monitoring of spiking activity across large populations of individual neurons. Here we propose a novel, inorganic class of fluorescent voltage sensors: semiconductor nanoparticles, such as ultrabright quantum dots (qdots). Our calculations revealed that transmembrane electric fields characteristic of neuronal spiking (~10 mV/nm) modulate a qdot's electronic structure and can induce ~5% changes in its fluorescence intensity and ~1 nm shifts in its emission wavelength, depending on the qdot's size, composition, and dielectric environment. Moreover, tailored qdot sensors composed of two different materials can exhibit substantial (~30%) changes in fluorescence intensity during neuronal spiking. Using signal detection theory, we show that conventional qdots should be capable of reporting voltage dynamics with millisecond precision across several tens or more individual neurons over a range of optical and neurophysiological conditions. These results unveil promising avenues for imaging spiking dynamics in neural networks and merit in-depth experimental investigation. Toward addressing these challenges, we studied whether tools from nanotechnology, specifically, bright, multifunctional semiconductor quantum dots (qdots), 22,23 might be useful for imaging neuronal membrane potentials. Qdots are known to possess voltagesensitive optical properties, including a red-shifting of the qdot's fluorescence emission peak, spectral broadening, and a decrease in the intensity of fluorescence emission ( Figure 1C,D). [24][25][26][27] Qdots also are highly resistant to photobleaching and exhibit large quantum yields and absorption cross sections for one-(σ 1 ) and two-photon (σ 2 ) excitation. For example, CdSe qdots with radius R ~ 3 nm exhibit cross sections of σ 1 > 1 nm 2 and σ 2 > 3 × 10 4 GM, as compared to σ 1 ~ 10 −2 nm 2 and σ 2 ~ 3 × 10 2 GM for green fluorescent protein. 28,29 Marshall and Schnitzer Page 2 ACS Nano. Author manuscript; available in PMC 2017 December 15. Graphical Abstract HHMI Author Manuscript HHMI Author Manuscript HHMI Author ManuscriptTo evaluate the spike detection capabilities of qdot indicators quantitatively, we applied a theoretical approach that incorporates the physical, biophysical, and statistical components of the problem. We calculated the effect of applied electric fields on the qdot's electronic structure and examined how this modulates a qdot's fluorescence intensity and emission spectra. We also studied nonspherical, nonhomogenous qdots, which we refer to more generally as semiconductor nanocrystals, and found that these nanoparticles can demonstrate muc...

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A hybrid approach to measuring electrical activity in genetically specified neurons

Cited by 166 publications

References 30 publications

Structural rearrangement of the intracellular domains during AMPA receptor activation

Structural rearrangement of the intracellular domains during AMPA receptor activation

Visualizing circuits and systems using transgenic reporters of neural activity

Optical Strategies for Sensing Neuronal Voltage Using Quantum Dots and Other Semiconductor Nanocrystals

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