Systems analysis of the single photon response in invertebrate photoreceptors

Alain Pumir, Jennifer Graves, Rama Ranganathan, Boris I. Shraiman

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Photoreceptors of Drosophila compound eye employ a G protein-mediated signaling pathway that transduces single photons into transient electrical responses called "quantum bumps" (QB). Although most of the molecular components of this pathway are already known, the system-level understanding of the mechanism of QB generation has remained elusive. Here, we present a quantitative model explaining how QBs emerge from stochastic nonlinear dynamics of the signaling cascade. The model shows that the cascade acts as an "integrate and fire" device and explains how photoreceptors achieve reliable responses to light although keeping low background in the dark. The model predicts the nontrivial behavior of mutants that enhance or suppress signaling and explains the dependence on external calcium, which controls feedback regulation. The results provide insight into physiological questions such as single-photon response efficiency and the adaptation of response to high incident-light level. The system-level analysis enabled by modeling phototransduction provides a foundation for understanding G protein signaling pathways less amenable to quantitative approaches.

Original languageEnglish (US)
Pages (from-to)10354-10359
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number30
StatePublished - Jul 29 2008


  • G protein-coupled receptor pathway
  • Phototransduction
  • Quantitative modeling

ASJC Scopus subject areas

  • General


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