Confocal imaging of [Ca2+] in cellular organelles by SEER, shifted excitation and emission ratioing of fluorescence

Launikonis, Bradley S., Zhou, Jing Song, Royer, Leandro, Shannon, Thomas R., Brum, Gustavo and Rios, Eduardo (2005) Confocal imaging of [Ca2+] in cellular organelles by SEER, shifted excitation and emission ratioing of fluorescence. Journal of Physiology, 567 2: 523-543. doi:10.1113/jphysiol.2005.087973

Author Launikonis, Bradley S.
Zhou, Jing Song
Royer, Leandro
Shannon, Thomas R.
Brum, Gustavo
Rios, Eduardo
Title Confocal imaging of [Ca2+] in cellular organelles by SEER, shifted excitation and emission ratioing of fluorescence
Journal name Journal of Physiology   Check publisher's open access policy
ISSN 0022-3751
Publication date 2005-09-01
Sub-type Article (original research)
DOI 10.1113/jphysiol.2005.087973
Volume 567
Issue 2
Start page 523
End page 543
Total pages 21
Place of publication Oxford, England
Publisher Blackwell for the Physiological Society
Language eng
Subject 320000 Medical and Health Sciences
Abstract Intracellular calcium signals regulate multiple cellular functions. They depend on release of Ca2+ from cellular stores into the cytosol, a process that appears to be tightly controlled by changes in [Ca2+] within the store. A method to image free [Ca2+] within cellular organelles was devised, which provided the first quantitative confocal images of [Ca2+] inside the sarcoplasmic reticulum (SR) of skeletal muscle. The method exploits, for greater sensitivity, the dual spectral shifts that some fluorescent dyes undergo upon binding Ca2+. It was implemented with mag-indo-1 trapped in the intracellular organelles of frog skeletal muscle and validated showing that it largely monitors [Ca2+] in a caffeine-sensitive compartment with the structure of the SR cisternae. A tentative calibration in situ demonstrated an increase in the dye's dissociation constant, not unlike that observed for other dyes in cellular environments. This increase, together with other characteristics of the ratioing method, placed the half-signal [Ca2+] near 1 mm, a value suitable for cellular stores. Demonstrated advantages of the technique include accuracy (that of a calibrated ratiometric method), dynamic range and sensitivity (from the combination of two spectral shifts), spatial and temporal resolution, and compatibility with a vast array of visible dyes to monitor diverse aspects of cellular function. SEER (shifted excitation and emission ratioing) also provides a [Ca2+] -independent measure of dye concentration in the cell. Store and mitochondrial [Ca2+] ([Ca2+](SR) and [Ca2+](mito)) could be measured separately using the high spatial resolution of SEER. Evolution of [Ca2+](SR) was followed upon changes in cytosolic [Ca2+]([Ca2+](cyto)). At [Ca2+](cyto) = 100nm, [Ca2+](mito) remained near the lower limit of detection and [Ca 21+] SR stabilized at values that were submillimolar according to our tentative calibration. Steady [Ca2+](SR) was only slightly higher in 800 nm [Ca2+](cyto), and essentially did not decrease unless [Ca2+](cyto) was reduced below 10 nm. While the increase of [Ca2+](SR) was limited by loss through Ca2+ release channels, its decrease in low [Ca2+](cyto) was largely dependent on leaks through the SR Ca2+ pump.
Keyword Physiology
Skeletal-muscle Fibers
Sarcoplasmic-reticulum Calcium
Luminal Calcium
Release Channel
Cane Toad
Q-Index Code C1

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
School of Biomedical Sciences Publications
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Citation counts: TR Web of Science Citation Count  Cited 42 times in Thomson Reuters Web of Science Article | Citations
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Created: Thu, 20 Sep 2007, 04:20:38 EST