Biology subjects

Korkotian, E.

Publications and source records attributed to Korkotian, E..

3 recordsLinked to original sources

bioRxiv2026

Synaptic Input Triggers On-Demand Spine-Specific Mitochondrial ATP Production and Delivery

Synaptic activity imposes acute energy demands, especially for restoring ionic gradients via pumps and exchangers that require ATP. While mitochondria are positioned near dendritic spines to meet this demand, how ATP is produced and delivered with spatial precision remains unclear. Here, using high-resolution calcium and ATP imaging, immuno-cytochemistry, and computational modeling, we demonstrate that synaptic input--but not back-propagating action potentials (bAPs)--triggers on-demand mitochondrial ATP production. This occurs only in spines containing a spine apparatus (SA), where calcium-induced calcium release (CICR) activates mitochondrial calcium uniporters (MCUs), initiating ATP synthesis. We show that ATP delivery is spatially constrained to mitochondrial regions facing the spine base, where ATP-synthase is enriched. Importantly, ATP produced elsewhere on the mitochondrial surface tends to diffuse into the dendrite. We further demonstrate that the delivery of ATP to the spine head is geometrically optimized: an intermediate spine neck length maximizes delivery efficiency. Mathematical modeling and simulations revealb that the time scale for ATP to reach and refill all head-localized exchangers is on the order of hundreds of milliseconds--fast enough to meet local metabolic needs. The present findings establish a mechanism in which nanoscale calcium signaling and mitochondrial architecture together ensure rapid, spatially targeted ATP delivery, tightly coupled to synaptic activity.

neuroscience↗

bioRxiv2021

Nanoscale organization and calcium influx in dendritic spines guarantee ER store refilling without depletion

Dendritic spines are critical components of the neuronal synapse as they receive and transform the synaptic input into a succession of biochemical events regulated by calcium signaling. The spine apparatus (SA), an extension of smooth endoplasmic reticulum (ER), regulates slow and fast calcium dynamics in spines. Calcium release events from SA result in a rapid depletion of calcium ion reservoir, yet the next cycle of signaling requires replenishment of SA calcium stores. How dendritic spines achieve this without triggering calcium release remains unclear. Using computational modeling, calcium and STED super-resolution imaging, we showed that the refilling of calcium-deprived SA involves store-operated calcium entry during spontaneous calcium transients in spine heads. We identified two main conditions that guarantee SA replenishment without depletion: (1) a small amplitude and slow timescale for calcium influx, and (2) a close proximity between SA and plasma membranes. Thereby, molecular nano-organization creates the conditions for a clear separation between SA replenishment and depletion. We further conclude that the nanoscale organization of SA receptors underlies the specificity of calcium dynamics patterns during the induction of long-term synaptic changes.

neuroscience↗

bioRxiv2018

Fast calcium transients in neuronal spines is driven by extreme statistics

Extreme statistics describe the distribution of rare events that can define the timescales of transduction within cellular microdomains. We combine biophysical modeling and analysis of live-cell calcium imaging to explain the fast calcium transient in spines. We show that in the presence of a spine apparatus (SA), which is an extension of the smooth endoplasmic reticulum (ER), calcium transients during synaptic inputs rely on rare and extreme calcium ion trajectories. Using numerical simulations, we predicted the asymmetrical distributions of Ryanodine receptors and SERCA pumps that we confirmed experimentally. When calcium ions are released in the spine head, the fastest ions arriving at the base determine the transient timescale through a calcium-induced calcium release mechanism. In general, the fastest particles arriving at a small target are likely to be a generic mechanism that determines the timescale of molecular transduction in cellular neuroscience.\n\nSignificance statementIntrigued by fast calcium transients of few milliseconds in dendritic spines, we investigated its underlying biophysical mechanism. We show here that it is generated by the diffusion of the fastest calcium ions when the spine contains a Spine Apparatus, an extension of the endoplasmic reticulum. This timescale is modulated by the initial number of released calcium ions and the asymmetric distribution of its associated calcium release associated Ryanodyne receptors, present only at the base of a spine. This novel mechanism of calcium signaling that we have unraveled here is driven by the fastest particles. To conclude, the rate of arrival of the fastest particles (ions) to a small target receptor defines the timescale of activation instead of the classical forward rate of chemical reactions introduced by von Smoluchowski in 1916. Applying this new rate theory to transduction should refine our understanding of the biophysical mechanisms underlying molecular signaling.

cell biology↗