IP₃-mediated Ca²⁺ transfer from ER to mitochondria stimulates ATP synthesis in primary hippocampal neurons

During electrical activity, Ca²⁺ enhances mitochondrial ATP production, helping to replenish the energy consumed during this process. Most Ca²⁺ enters the cell via ligand- or voltage-gated channels on the neuronal membrane, where it stimulates the release of additional Ca²⁺ from the endoplasmic reticulum (ER). Although the influence of cytosolic Ca²⁺ on neuronal metabolism has been widely investigated, relatively few studies have explored the contribution of ER Ca²⁺ release in this context. Therefore, we investigated how activity-driven Ca²⁺ crosstalk between the ER and mitochondria influences the regulation of mitochondrial ATP production. We show that in primary hippocampal neurons derived from rat pups of either sex, depletion of ER Ca²⁺ led to a reduction in mitochondrial Ca²⁺ levels during both resting and stimulated states, while exerting only a minimal impact on cytosolic Ca²⁺ levels. Additionally, impaired ER-mitochondria Ca²⁺ transfer led to a reduction in mitochondrial ATP production. Similar effects were observed when inositol-3-phosphate receptors (IP₃Rs), but not ryanodine receptors (RyRs), were pharmacologically inhibited. Together, our findings show that, in hippocampal neurons, Ca²⁺ is transferred from the ER to mitochondria through IP₃ receptors, and this Ca²⁺ crosstalk in turn enhances mitochondrial ATP production in response to neuronal activity.