Spontaneous Ca²⁺ Fluctuations Arise in Thin Astrocytic Processes With Real 3D Geometry

Area of Science:

• Neuroscience
• Cellular Biology
• Computational Modeling

Background:

• Astrocytes play a key role in neuronal function through calcium (Ca²⁺) signaling.
• Spontaneous astrocytic Ca²⁺ oscillations are implicated in neuronal synchronized activities like epilepsy and slow-wave rhythms.
• The mechanisms underlying spontaneous astrocytic Ca²⁺ oscillations remain poorly understood.

Purpose of the Study:

• To investigate the mechanisms driving spontaneous Ca²⁺ oscillations in astrocytes.
• To explore the role of astrocytic geometry and ion transporter dynamics in Ca²⁺ signaling.
• To model Ca²⁺ oscillations using realistic 3D synapse structures.

Main Methods:

• Developed a computational model incorporating 3D synapse geometries from electron microscopy data.
• Included kinetic data for astrocytic glutamate transporters (EAATs) and the Na⁺/Ca²⁺ exchanger (NCX).
• Simulated spontaneous Ca²⁺ oscillations under varying conditions of astrocytic process geometry and intracellular Na⁺ concentration.

Main Results:

• The surface/volume ratio (SVR) of peri-synaptic astrocytic processes was identified as a critical determinant for NCX-mediated spontaneous Ca²⁺ oscillations.
• Increased intracellular astrocytic Na⁺ concentration was shown to facilitate the emergence of Ca²⁺ fluctuations.
• Model simulations confirmed the generation of stable, spontaneous Ca²⁺ oscillations driven by NCX activity.

Conclusions:

• Astrocytic Ca²⁺ oscillations are significantly influenced by the physical shape of astrocytic processes.
• Intracellular Na⁺ dynamics play a crucial role in regulating astrocytic Ca²⁺ signaling.
• Dynamical reshaping of astrocyte processes is fundamental for generating and propagating intrinsic Ca²⁺ oscillations.