UC San Diego

Intracellular calcium (Ca2+) signaling can regulate synaptic plasticity via gene expression in neurons. One pathway that links Ca2+ to gene expression is the G-protein coupled receptor - inositol triphosphate receptor (GPCR-IP3R) pathway. Ca2+ signaling dynamics could be affected spatiotemporally by subcellular ultrastructure, such as the endoplasmic reticulum (ER) and distributions of Ca2+-regulating proteins in the GPCR-IP3R pathway. Computational models have been built to better understand intracellular Ca2+ signaling but have yet to consider accurate neuronal ultrastructure and protein localizations. In order to make a precise model simulating neuronal Ca2+ dynamics, we aimed to analyze realistic somatic ultrastructure and distributions of signaling proteins in the GPCR-IP3R pathway within cerebellar Purkinje neurons. Here, using electron microscopy, we found out that the sub-surface ERs are denser and mostly parallel to the plasma membrane (PM). We performed immunohistochemistry for multiple proteins in the GPCR (coupled to Gαq subunit) signaling pathway, but none of these proteins showed prominent asymmetries except for IP3R. In the initial model with idealized geometry, we found out that specific ER membrane structure organization near the PM may facilitate local Ca2+ concentration increases. In addition, heterogeneous IP3R distribution could lead to various degrees of Ca2+ release from the internal ER Ca2+ store. Based on the results above, we concluded that the unique ER organization and heterogeneous Ca2+-signaling protein distributions may shape Ca2+ signaling dynamics within the Purkinje somas.