Disruption of actin cytoskeleton causes internalization of Ca(v)1.3 (alpha 1D) L-type calcium channels in salamander retinal neurons.

Purpose: To study the influence of actin cytoskeleton reorganization on the subcellular distribution of Ca(v)1.3 L-type Ca2+ channels in salamander retinal third-order neurons.

Methods: Immunocytochemistry with confocal microscopy was used to demonstrate internalization of the Ca(v)1.3 isoform of L-type voltage-gated Ca2+ channels in third-order retinal neurons. A specificity of antibody was confirmed with Western blotting and in control experiments preabsorbing antibody wit its respective peptide. Whole-cell patch clamp technique was applied to record L-type currents from ganglion cells in slice preparations in the presence of N- and P/Q type Ca2+ channel blockers.

Results: A high level of Ca(v)1.3 labeling was present in cone photoreceptor terminals in the outer plexiform layer (OPL), as aggregates of puncta. Punctate Ca(v)1.3 labeling was evident throughout the IPL and around the cell bodies in the outer nuclear (ONL), inner nuclear (INL) and on somas and axons of ganglion cells labeled with rhodamine-conjugated dextran. Doubly labeled sections for synaptophysin and Ca(v)1.3 revealed colocalization in the OPL and IPL. Depolymerization of the actin cytoskeleton caused a dynamin-dependent internalization of Ca(v)1.3 but not Ca(v)1.2 subtype of voltage-gated Ca2+ channels in dissociated neurons. In ganglion cells, the inhibition of L-type Ca2+ currents by F-actin disrupters was mediated by Ca2+ channel internalization. Treatment with cytochalasin D protected retinal neurons against kainate-induced excitotoxicity.

Conclusions: Actin cytoskeleton dynamics plays an important role in the regulation of subcellular distribution and function of Ca(v)1.3 L-type Ca2+ channels in salamander retinal neurons. Ca2+-dependent actin depolymerization may serve as a negative feedback mechanism to reduce excessive Ca2+ influx and thereby protect neurons against glutamate-induced excitotoxicity.