Dataset Information

Superresolution localization of single functional IP3R channels utilizing Ca2+ flux as a readout.

ABSTRACT: The subcellular localization of membrane Ca2+ channels is crucial for their functioning, but is difficult to study because channels may be distributed more closely than the resolution of conventional microscopy is able to detect. We describe a technique, stochastic channel Ca2+ nanoscale resolution (SCCaNR), employing Ca2+-sensitive fluorescent dyes to localize stochastic openings and closings of single Ca2+-permeable channels within <50 nm, and apply it to examine the clustered arrangement of inositol trisphosphate receptor (IP3R) channels underlying local Ca2+ puffs. Fluorescence signals (blips) arising from single functional IP3Rs are almost immotile (diffusion coefficient<0.003 microm2 s(-1)), as are puff sites over prolonged periods, suggesting that the architecture of this signaling system is stable and not subject to rapid, dynamic rearrangement. However, rapid stepwise changes in centroid position of fluorescence are evident within the durations of individual puffs. These apparent movements likely result from asynchronous gating of IP3Rs distributed within clusters that have an overall diameter of approximately 400 nm, indicating that the nanoscale architecture of IP3R clusters is important in shaping local Ca2+ signals. We anticipate that SCCaNR will complement superresolution techniques such as PALM and STORM for studies of Ca2+ channels as it obviates the need for photoswitchable labels and provides functional as well as spatial information.

SUBMITTER: Wiltgen SM

PROVIDER: S-EPMC2905071 | biostudies-literature | 2010 Jul

REPOSITORIES: biostudies-literature

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Superresolution localization of single functional IP3R channels utilizing Ca2+ flux as a readout.

Wiltgen Steven M SM Smith Ian F IF Parker Ian I

Biophysical journal 20100701 2

The subcellular localization of membrane Ca2+ channels is crucial for their functioning, but is difficult to study because channels may be distributed more closely than the resolution of conventional microscopy is able to detect. We describe a technique, stochastic channel Ca2+ nanoscale resolution (SCCaNR), employing Ca2+-sensitive fluorescent dyes to localize stochastic openings and closings of single Ca2+-permeable channels within <50 nm, and apply it to examine the clustered arrangement of i ...[more]

PMID: 20643061

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Project description:We describe an optical technique using total internal reflection fluorescence (TIRF) microscopy to obtain simultaneous and independent recordings from numerous ion channels via imaging of single-channel Ca2+ flux. Muscle nicotinic acetylcholine (ACh) receptors made up of alphabetagammadelta subunits were expressed in Xenopus oocytes, and single channel Ca2+ fluorescence transients (SCCaFTs) were imaged using a fast (500 fps) electron-multiplied c.c.d. camera with fluo-4 as the indicator. Consistent with their arising through openings of individual nicotinic channels, SCCaFTs were seen only when a nicotinic agonist was present in the bathing solution, were blocked by curare, and increased in frequency as roughly the second power of [ACh]. Their fluorescence amplitudes varied linearly with membrane potential and extrapolated to zero at about +60 mV. The rise and fall times of fluorescence were as fast as 2 ms, providing a kinetic resolution adequate to characterize channel gating kinetics; which showed mean open times of 7.9 and 15.8 ms when activated, respectively, by ACh or suberyldicholine. Simultaneous records were obtained from >400 channels in the imaging field, and we devised a novel "channel chip" representation to depict the resultant large dataset as a single image. The positions of SCCaFTs remained fixed (<100 nm displacement) over tens of seconds, indicating that the nicotinic receptor/channels are anchored in the oocyte membrane; and the spatial distribution of channels appeared random without evidence of clustering. Our results extend single-channel TIRFM imaging to ligand-gated channels that display only partial permeability to Ca2+, and demonstrate an order-of-magnitude improvement in kinetic resolution. We believe that functional single-channel imaging opens a new approach to ion channel study, having particular advantages over patch-clamp recording in that it is massively parallel, and provides high-resolution spatial information that is inaccessible by electrophysiological techniques.

Project description:To be able to resolve molecular-clusters it is crucial to access vital information (such as, molecule density, cluster-size, and others) that are key in understanding disease progression and the underlying mechanism. Traditional single-molecule localization microscopy (SMLM) techniques use molecules of variable sizes (as determined by its localization precision (LP)) to reconstruct a super-resolution map. This results in an image with overlapping and superimposing PSFs (due to a wide size-spectrum of single-molecules) that undermine image resolution. Ideally, it should be possible to identify the brightest molecules (also termed as the fortunate molecules) to reconstruct ultra-superresolution map, provided sufficient statistics is available from the recorded data. Probabilistic Optically-Selective Single-molecule Imaging Based Localization Encoded (POSSIBLE) microscopy explores this possibility by introducing a narrow probability size-distribution of single-molecules (narrow size-spectrum about a predefined mean-size). The reconstruction begins by presetting the mean and variance of the narrow distribution function (Gaussian function). Subsequently, the dataset is processed and single-molecules are filtered by the Gaussian function to remove unfortunate molecules. The fortunate molecules thus retained are then mapped to reconstruct an ultra-superresolution map. In-principle, the POSSIBLE microscopy technique is capable of infinite resolution (resolution of the order of actual single-molecule size) provided enough fortunate molecules are experimentally detected. In short, bright molecules (with large emissivity) holds the key. Here, we demonstrate the POSSIBLE microscopy technique and reconstruct single-molecule images with an average PSF sizes of σ ± Δσ = 15 ± 10 nm, 30 ± 2 nm & 50 ± 2 nm. Results show better-resolved Dendra2-HA clusters with large cluster-density in transfected NIH3T3 fibroblast cells as compared to the traditional SMLM techniques. Cluster analysis indicates densely-packed HA molecules, HA-HA interaction, and a surge in the number of HA molecules per cluster post 24 Hrs of transfection. The study using POSSIBLE microscopy introduces new insights in influenza biology. We anticipate exciting applications in the multidisciplinary field of disease biology, oncology, and biomedical imaging.

Dataset Information

Superresolution localization of single functional IP3R channels utilizing Ca2+ flux as a readout.

Publications

Superresolution localization of single functional IP3R channels utilizing Ca2+ flux as a readout.

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