Measuring calcium signaling using genetically targetable fluorescent indicators.
Genetically encoded Ca2+ indicators allow researchers to quantitatively measure Ca2+ dynamics in a variety of experimental systems. This protocol summarizes the indicators that are available, and highlights those that are most appropriate for a number of experimental conditions, such as measuring Ca2+ in specific organelles and localizations in mammalian tissue-culture cells. The protocol itself focuses on the use of a cameleon, which is a fluorescence resonance-energy transfer (FRET)-based indicator comprising two fluorescent proteins and two Ca2+-responsive elements (a variant of calmodulin (CaM) and a CaM-binding peptide). This protocol details how to set up and conduct a Ca2+-imaging experiment, accomplish offline data processing (such as background correction) and convert the observed FRET ratio changes to Ca2+ concentrations. Additionally, we highlight some of the challenges in observing organellar Ca2+ and the alternative strategies researchers can employ for effectively calibrating the genetically encoded Ca2+ indicators in these locations. Setting up and conducting an initial calibration of the microscope system is estimated to take approximately 1 week, assuming that all the component parts are readily available. Cell culture and transfection is estimated to take approximately 3 d (from the time of plating cells on imaging dishes). An experiment and calibration will probably take a few hours. Finally, the offline data workup can take approximately 1 d depending on the extent of analysis.
Palmer
Amy E
AE
Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, USA. amy.palmer@colorado.edu
Tsien
Roger Y
RY
D000818:Animals; D015415:Biomarkers / Q000032:analysis* / Q000378:metabolism; D002118:Calcium / Q000032:analysis* / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000378:metabolism; D002478:Cells, Cultured; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods*; D005456:Fluorescent Dyes / Q000378:metabolism*; D008856:Microscopy, Fluorescence / Q000295:instrumentation / Q000379:methods
D015415:Biomarkers; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D005456:Fluorescent Dyes; D002118:Calcium