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Melanopsin ganglion cells use a membrane-associated rhabdomeric phototransduction cascade

Dustin M Graham1, Kwoon Y Wong, Peter Shapiro

  • 1Department of Neuroscience, Brown University, Providence, RI 02912, USA.

Journal of Neurophysiology
|February 29, 2008
PubMed

Insights

Intrinsically photosensitive retinal ganglion cells (ipRGCs) use a phosphoinositide cascade for phototransduction, similar to invertebrate eyes. This discovery reveals the signaling pathway for melanopsin in these light-sensing cells.

Area of Science:

  • Neuroscience
  • Cell Biology
  • Vision Science

Background:

  • Intrinsically photosensitive retinal ganglion cells (ipRGCs) are key photoreceptors in the mammalian eye.
  • These cells regulate vital functions like pupil constriction and circadian rhythms.
  • The photopigment melanopsin mediates these responses, but its signaling pathway remains unclear.

Purpose of the Study:

  • To elucidate the phototransduction signaling cascade in ipRGCs.
  • To identify the molecular mechanisms by which melanopsin triggers a photocurrent.
  • To compare the ipRGC phototransduction pathway with known photoreceptor mechanisms.

Main Methods:

  • Patch-clamp recordings were performed on dissociated ipRGCs in culture.
  • Single-cell RT-PCR and immunofluorescence confirmed the presence of signaling molecules.
  • Experiments utilized excised inside-out patches of ipRGC membrane to assess the photoresponse.

Main Results:

  • Illumination of ipRGCs activated a G(q/11) class G protein, initiating a phosphoinositide cascade.
  • The effector enzyme phospholipase C was stimulated upon melanopsin activation.
  • The photoresponse was functional in isolated membrane patches, localizing core components to the plasma membrane.

Conclusions:

  • The phototransduction mechanism in ipRGCs relies on a membrane-associated phosphoinositide cascade.
  • This pathway is remarkably similar to that found in invertebrate rhabdomeric photoreceptors.
  • These findings support an evolutionary link between ipRGCs and invertebrate photoreceptors.

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