Carbenoxolone blocks the light-evoked rise in intracellular calcium in isolated melanopsin ganglion cell photoreceptors

PLoS One. 2011;6(7):e22721. doi: 10.1371/journal.pone.0022721. Epub 2011 Jul 29.


Background: Retinal ganglion cells expressing the photopigment melanopsin are intrinsically photosensitive (ipRGCs). These ganglion cell photoreceptors send axons to several central targets involved in a variety of functions. Within the retina ipRGCs provide excitatory drive to dopaminergic amacrine cells via glutamatergic signals and ipRGCs are coupled to wide-field GABAergic amacrine cells via gap junctions. However, the extent to which ipRGCs are coupled to other retinal neurons in the ganglion cell layer via gap junctions is unclear. Carbenoxolone, a widely employed gap junction inhibitor, greatly reduces the number of retinal neurons exhibiting non-rod, non-cone mediated light-evoked Ca(2+) signals suggesting extensive intercellular coupling between ipRGCs and non-ipRGCs in the ganglion cell layer. However, carbenoxolone may directly inhibit light-evoked Ca(2+) signals in ipRGCs independent of gap junction blockade.

Methodology/principal findings: To test the possibility that carbenoxolone directly inhibits light-evoked Ca(2+) responses in ipRGCs, the light-evoked rise in intracellular Ca(2+) ([Ca(2+)](i)) was examined using fura-2 imaging in isolated rat ipRGCs maintained in short-term culture in the absence and presence of carbenoxolone. Carbenoxolone at 50 and 100 µM concentrations completely abolished the light-evoked rise in [Ca(2+)](i) in isolated ipRGCs. Recovery from carbenoxolone inhibition was variable.

Conclusions/significance: We demonstrate that the light-evoked rise in [Ca(2+)](i) in isolated mammalian ganglion cell photoreceptors is inhibited by carbenoxolone. Since the light-evoked increase in [Ca(2+)](i) in isolated ipRGCs is almost entirely due to Ca(2+) entry via L-type voltage-gated calcium channels and carbenoxolone does not inhibit light-evoked action potential firing in ipRGCs in situ, carbenoxolone may block the light-evoked increase in [Ca(2+)](i) in ipRGCs by blocking L-type voltage-gated Ca(2+) channels. The ability of carbenoxolone to block evoked Ca(2+) responses must be taken into account when interpreting the effects of this pharmacological agent on retinal or other neuronal circuits, particularly if a change in [Ca(2+)](i) is the output being measured.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Action Potentials / drug effects
  • Animals
  • Anti-Ulcer Agents / pharmacology
  • Calcium / metabolism*
  • Carbenoxolone / pharmacology*
  • Cells, Cultured
  • Fura-2
  • Immunoglobulin G / immunology
  • Light*
  • Peptide Fragments / immunology
  • Photic Stimulation
  • Photoreceptor Cells / drug effects
  • Photoreceptor Cells / metabolism*
  • Rabbits
  • Rats
  • Rats, Long-Evans
  • Retina / cytology
  • Retina / drug effects
  • Retina / metabolism
  • Retinal Ganglion Cells / drug effects*
  • Retinal Ganglion Cells / metabolism*
  • Retinal Ganglion Cells / radiation effects
  • Rod Opsins / immunology
  • Rod Opsins / metabolism*


  • Anti-Ulcer Agents
  • Immunoglobulin G
  • Peptide Fragments
  • Rod Opsins
  • melanopsin
  • Carbenoxolone
  • Calcium
  • Fura-2