An improved genetically encoded red fluorescent Ca2+ indicator for detecting optically evoked action potentials

PLoS One. 2012;7(7):e39933. doi: 10.1371/journal.pone.0039933. Epub 2012 Jul 10.


Genetically encoded Ca(2+) indicators (GECIs) are powerful tools to image activities of defined cell populations. Here, we developed an improved red fluorescent GECI, termed R-CaMP1.07, by mutagenizing R-GECO1. In HeLa cell assays, R-CaMP1.07 exhibited a 1.5-2-fold greater fluorescence response compared to R-GECO1. In hippocampal pyramidal neurons, R-CaMP1.07 detected Ca(2+) transients triggered by single action potentials (APs) with a probability of 95% and a signal-to-noise ratio >7 at a frame rate of 50 Hz. The amplitudes of Ca(2+) transients linearly correlated with the number of APs. The expression of R-CaMP1.07 did not significantly alter the electrophysiological properties or synaptic activity patterns. The co-expression of R-CaMP1.07 and channelrhodpsin-2 (ChR2), a photosensitive cation channel, in pyramidal neurons demonstrated that R-CaMP1.07 was applicable for the monitoring of Ca(2+) transients in response to optically evoked APs, because the excitation light for R-CaMP1.07 hardly activated ChR2. These technical advancements provide a novel strategy for monitoring and manipulating neuronal activity with single cell resolution.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / physiology*
  • Action Potentials / radiation effects
  • Animals
  • Animals, Newborn
  • Calcium / analysis*
  • Calcium / metabolism
  • Channelrhodopsins
  • Escherichia coli
  • Fluorescent Dyes
  • Gene Expression
  • Genes, Reporter*
  • HeLa Cells
  • Humans
  • Light
  • Molecular Probes*
  • Neurons / physiology*
  • Neurons / radiation effects
  • Pyramidal Cells / physiology*
  • Pyramidal Cells / radiation effects
  • Rats
  • Rats, Wistar
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Signal-To-Noise Ratio
  • Single-Cell Analysis
  • Transgenes


  • Channelrhodopsins
  • Fluorescent Dyes
  • Molecular Probes
  • Recombinant Proteins
  • Calcium