Blockade of RyRs in the ER Attenuates 6-OHDA-Induced Calcium Overload, Cellular Hypo-Excitability and Apoptosis in Dopaminergic Neurons.

Calcium (Ca) dyshomeostasis induced by endoplasmic reticulum (ER) stress is an important molecular mechanism of selective dopaminergic (DA) neuron loss in Parkinson's disease (PD). Inositol 1,4,5-triphosphate receptors (IPRs) and ryanodine receptors (RyRs), which are located on the ER surface, are the main endogenous Ca release channels and play crucial roles in regulating Ca homeostasis. However, the roles of these endogenous Ca release channels in PD and their effects on the function and survival of DA neurons remain unknown. In this study, using a 6-hydroxydopamine (6-OHDA)-induced PD model (SN4741 Cell line), we found that 6-OHDA significantly increased cytoplasmic Ca levels ([Ca2+]), which was attenuated by pretreatment with 4-phenyl butyric acid (4-PBA; an ER stress inhibitor) or ryanodine (a RyRs blocker). In addition, in acute midbrain slices of male Sprague-Dawley rats, we found that 6-OHDA reduced the spike number and rheobase of DA neurons, which were also reversed by pretreatment with 4-PBA and ryanodine. TUNEL staining and MTT assays also showed that 4-PBA and ryanodine obviously alleviated 6-OHDA-induced cell apoptosis and devitalization. Interestingly, a IPRs blocker had little effect on the above 6-OHDA-induced neurotoxicity in DA neurons. In conclusion, our findings provide evidence of the different roles of IPRs and RyRs in the regulation of endogenous Ca homeostasis, neuronal excitability, and viability in DA neurons, and suggest a potential therapeutic strategy for PD by inhibiting the RyRs Ca channels in the ER.