BPS2026 – Biophysically constrained computational model of mitochondrial Ca2+ uniporter gating and kinetics and mitochondrial Ca2+ dynamics

Mitochondrial Ca 2+ uptake through the mitochondrial Ca 2+ uniporter (MCU) plays a key role in regulating mitochondrial Ca 2+ dynamics and coupling cytosolic Ca 2+ transients to mitochondrial oxidative metabolism. MCU activity is regulated by cytosolic Ca 2+ and Mg 2+ levels as well as by feedback from matrix Ca 2+ , but a unified quantitative model that integrates these mechanisms and links them to mitochondrial Ca 2+ dynamics is lacking. We developed a biophysically constrained mathematical model of MCU gating that incorporates cytosolic Ca 2+ activation via MICU1/2 and matrix Ca 2+ inhibition and reactivation via EMRE. The model provides a quantitative framework for computing Ca 2+ flux across the inner mitochondrial membrane (IMM) based on MCU gating state transitions. The model integrates three modules: (1) a 3-state cooperative Markov scheme for MICU1/2-mediated Ca 2+ -dependent activation, representing transitions between closed, partially open, and fully open MCU states; (2) a 3-state matrix-side EMRE module describing matrix Ca 2+ -dependent high-affinity inhibition and low-affinity reactivation; and (3) a thermodynamically consistent Ca 2+ flux expression dependent on mitochondrial membrane potential (ΔΨ m ), transmembrane Ca 2+ and Mg 2+ levels, and the fractional occupancy of conductive MCU states. The MCU model is further integrated with other mitochondrial cation transport modules to study mitochondrial Ca 2+ dynamics under different perturbations, including the knockout of MICU1/2. Model parameters were fit to mitochondrial Ca 2+ uptake data across a range of [Ca 2+ ], [Mg 2+ ], and ΔΨ m conditions. Simulations reproduce key features of MCU behavior—MICU-dependent thresholding, sharp Ca 2+ activation kinetics, Mg 2+ -induced sigmoidal Ca 2+ flux inhibition, and biphasic regulation by matrix Ca 2+ . Matrix Ca 2+ feedback dynamically tunes MCU availability, enabling rapid cytosolic response while limiting mitochondrial Ca 2+ overload during sustained signaling. This model offers a predictive and mechanistic framework for mitochondrial Ca 2+ handling and its integration with cellular bioenergetics.