Specialized cortical ER architecture modulates Ca²⁺ signaling dynamics

Ca²⁺ signaling is ubiquitous and supports a multitude of cellular events. Specificity in Ca²⁺ signaling is encoded in its spatial and temporal dynamics. Ca²⁺ tunneling regulates the dynamics of Ca²⁺ signals downstream of store operated Ca²⁺ entry (SOCE). Here, we describe a novel cortical ER (cER) architectural feature, that we call the cER-basket, which underpins Ca²⁺ tunneling. We discovered the cER-basket through a combination of 3D reconstructions of the cortical ER at the ultrastructural level coupled to mathematical modeling of Ca²⁺ tunneling. Using insights from the modeling to inform experimental approaches and vice versa, we show that the detailed structural features of the cER-basket support Ca²⁺ tunneling. Therefore, we report a specific cortical ER structure, the cER-basket, which modulates cellular Ca²⁺ dynamics.