Carbenoxolone Blocks the Light-Evoked Rise in Intracellular Calcium in Isolated Melanopsin Ganglion Cell Photoreceptors

Authors

Jayne R. Bramley, University of Nebraska-Lincoln
Erin M. Wiles, University of Nebraska-Lincoln
Patricia J. Sollars, University of Nebraska-LincolnFollow
Gary E. Pickard, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

2011

Citation

Bramley JR, Wiles EM, Sollars PJ, Pickard GE (2011) Carbenoxolone Blocks the Light-Evoked Rise in Intracellular Calcium in Isolated Melanopsin Ganglion Cell Photoreceptors. PLoS ONE 6(7): e22721. doi:10.1371/journal.pone.0022721

Comments

Copyright 2011 Bramley et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License.

Abstract

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 widefield 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 Ca²⁺ signals suggesting extensive intercellular coupling between ipRGCs and non-ipRGCs in the ganglion cell layer. However, carbenoxolone may directly inhibit light-evoked Ca²⁺ signals in ipRGCs independent of gap junction blockade.

Methodology/Principal Findings: To test the possibility that carbenoxolone directly inhibits light-evoked Ca²⁺ responses in ipRGCs, the light-evoked rise in intracellular Ca²⁺ ([Ca²⁺]_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 uM concentrations completely abolished the light-evoked rise in [Ca²⁺]_i in isolated ipRGCs. Recovery from carbenoxolone inhibition was variable.

Conclusions/Significance: We demonstrate that the light-evoked rise in [Ca²⁺]_i in isolated mammalian ganglion cell photoreceptors is inhibited by carbenoxolone. Since the light-evoked increase in [Ca²⁺]_i in isolated ipRGCs is almost entirely due to Ca²⁺ 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 [Ca²⁺]_i in ipRGCs by blocking L-type voltage-gated Ca²⁺ channels. The ability of carbenoxolone to block evoked Ca²⁺ 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 [Ca²⁺]_i is the output being measured.