Lateral diffusion of inositol 1,4,5-trisphosphate receptor type 1 in Purkinje cells is regulated by calcium and actin filaments

Inositol 1,4,5-trisphosphate receptor type 1 (IP₃R1) is an intracellular Ca²⁺ release channel that plays crucial roles in the functions of Purkinje cells. The dynamics of IP₃R1 on the endoplasmic reticulum membrane and the distribution of IP₃R1 in neurons are thought to be important for the spatial regulation of Ca²⁺ release. In this study, we analyzed the lateral diffusion of IP₃R1 in Purkinje cells in cerebellar slice cultures using fluorescence recovery after photobleaching. In the dendrites of Purkinje cells, IP₃R1 showed lateral diffusion with an effective diffusion constant of approximately 0.30 μm²/s, and the diffusion of IP₃R1 was negatively regulated by actin filaments. We found that actin filaments were also involved in the regulation of IP₃R1 diffusion in the spine of Purkinje cells. Glutamate or quisqualic acid stimulation, which activates glutamate receptors and leads to a Ca²⁺ transient in Purkinje cells, decreased the diffusion of IP₃R1 and increased the density of actin in spines. These findings indicate that the neuronal activity-dependent augmentation of actin contributes to the stabilization of IP₃R1 in spines.