Imaging local Ca2+ signals in cultured mammalian cells

J Vis Exp. 2015 Mar 3:(97):52516. doi: 10.3791/52516.

Abstract

Cytosolic Ca2+ ions regulate numerous aspects of cellular activity in almost all cell types, controlling processes as wide-ranging as gene transcription, electrical excitability and cell proliferation. The diversity and specificity of Ca2+ signaling derives from mechanisms by which Ca2+ signals are generated to act over different time and spatial scales, ranging from cell-wide oscillations and waves occurring over the periods of minutes to local transient Ca2+ microdomains (Ca2+ puffs) lasting milliseconds. Recent advances in electron multiplied CCD (EMCCD) cameras now allow for imaging of local Ca2+ signals with a 128 x 128 pixel spatial resolution at rates of >500 frames sec(-1) (fps). This approach is highly parallel and enables the simultaneous monitoring of hundreds of channels or puff sites in a single experiment. However, the vast amounts of data generated (ca. 1 Gb per min) render visual identification and analysis of local Ca2+ events impracticable. Here we describe and demonstrate the procedures for the acquisition, detection, and analysis of local IP3-mediated Ca2+ signals in intact mammalian cells loaded with Ca2+ indicators using both wide-field epi-fluorescence (WF) and total internal reflection fluorescence (TIRF) microscopy. Furthermore, we describe an algorithm developed within the open-source software environment Python that automates the identification and analysis of these local Ca2+ signals. The algorithm localizes sites of Ca2+ release with sub-pixel resolution; allows user review of data; and outputs time sequences of fluorescence ratio signals together with amplitude and kinetic data in an Excel-compatible table.

Publication types

  • Research Support, N.I.H., Extramural
  • Video-Audio Media

MeSH terms

  • Algorithms
  • Calcium / analysis*
  • Calcium / metabolism
  • Calcium Signaling*
  • Cell Line
  • Cell Line, Tumor
  • Cytosol / metabolism
  • Fluorescence
  • Humans
  • Inositol 1,4,5-Trisphosphate / analysis
  • Inositol 1,4,5-Trisphosphate / metabolism
  • Kinetics
  • Microscopy, Fluorescence / methods*
  • Software

Substances

  • Inositol 1,4,5-Trisphosphate
  • Calcium