Localization of Binding Proteins of Intracellular Calcium Channels in Mouse Retina Ganglion Cells

Abstract

Purpose: : Inositol–1, 4, 5–triphosphate receptors (IP₃Rs) are intracellular Ca²⁺ release channels that are critical components for controlling cytosolic Ca²⁺ concentrations and intracellular signaling pathways. In neurons, including retinal ganglion cells (RGCs), these IP₃R–regulated pathways include synaptic activity, gene expression, differentiation and apoptosis. The molecular substrates of such regulatory pathways controlling intracellular Ca²⁺ levels include IP₃R binding proteins. Identifying the localization of these accessory proteins which tightly control IP₃R function is critical for the understanding of RGC function under the control of Ca²⁺ signaling pathways.

Methods: : The expression of IP₃R–associated proteins CARP and FKBP12 by adult mouse RGCs was determined using immunoblotting, immunocytochemistry and specific antibodies. RGCs were identified by cell specific markers including neurofilament 68kDa Thy1.1 and Thy1.2.

Results: : Immunoreactivity for the IP₃R–associated proteins CARP and FKBP12 was detected on intracellular membranes of RGCs throughout the cells. Expression was co–localized with RGC markers and IP₃R subtypes 1, 2 and 3.

Conclusions: : The presence of critical IP₃R binding proteins in RGCs indicates that these proteins are localized in compartments that allow interaction with IP₃Rs and play a potential role in RGC calcium signaling. Expression and differential localization of IP₃R associated proteins may therefore be a molecular mechanism used by RGC Ca²⁺ signaling. These findings allow us to identify the involvement of IP₃R–mediated Ca²⁺ signaling in RGC physiology and to develop neuroprotective strategies for RGCs targeting Ca²⁺–mediated cell toxicity.

Keywords: ion channels • retina: proximal (bipolar, amacrine, and ganglion cells) • immunohistochemistry