Glutamate-induced internalization of Cav1.3 L-type Ca2+ channels protects retinal neurons against excitotoxicity

摘要

Glutamate-induced rise in the intracellular Ca²⁺ level is thought to be a major cause of excitotoxic cell death, but the mechanisms that control the Ca²⁺ overload are poorly understood. Using immunocytochemistry, electrophysiology and Ca²⁺ imaging, we show that activation of ionotropic glutamate receptors induces a selective internalization of Cav1.3 L-type Ca²⁺ channels in salamander retinal neurons. The effect of glutamate on Cav1.3 internalization was blocked in Ca²⁺-free external solution, or by strong buffering of internal Ca²⁺ with BAPTA. Downregulation of L-type Ca²⁺ channel activity in retinal ganglion cells by glutamate was suppressed by inhibitors of dynamin-dependent endocytosis. Stabilization of F-actin by jasplakinolide significantly reduced the ability of glutamate to induce internalization suggesting it is mediated by Ca²⁺-dependent reorganization of actin cytoskeleton. We showed that the Cav1.3 is the primary L-type Ca²⁺ channel contributing to kainate-induced excitotoxic death of amacrine and ganglion cells. Block of Cav1.3 internalization by either dynamin inhibition or F-actin stabilization increased vulnerability of retinal amacrine and ganglion cells to kainate-induced excitotoxicity. Our data show for the first time that Cav1.3 L-type Ca²⁺ channels are subject to rapid glutamate-induced internalization, which may serve as a negative feedback mechanism protecting retinal neurons against glutamate-induced excitotoxicity.