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Calcium Dynamics in Dendritic Spines and Spine Motility

D. Holcman ^*, Z. Schuss  and E. Korkotian 

^* Department of Mathematics, Weizmann Institute of Science, Rehovot, Israel, and Keck Center for Integrative Neuroscience, Department of Physiology, University of California at San Francisco, San Francisco, California; Department of Mathematics, Tel Aviv University, Ramat-Aviv, Tel-Aviv, Israel; and Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel

Correspondence: Address reprint requests to D. Holcman, Keck Center for Integrative Neuroscience, Department of Physiology, UCSF, 513 Parnassus Ave., San Francisco, CA 94143-0444. Tel.: 415-476-4601; E-mail: holcman{at}phy.ucsf.edu.

A dendritic spine is an intracellular compartment in synapses of central neurons. The role of the fast twitching of spines, brought about by a transient rise of internal calcium concentration above that of the parent dendrite, has been hitherto unclear. We propose an explanation of the cause and effect of the twitching and its role in the functioning of the spine as a fast calcium compartment. Our molecular model postulates that rapid spine motility is due to the concerted contraction of calcium-binding proteins. The contraction induces a stream of cytoplasmic fluid in the direction of the dendritic shaft, thus speeding up the time course of spine calcium dynamics, relative to pure diffusion. Simulations indicate that chemical reaction rate theory at the molecular level can explain spine motility. They reveal two time periods in calcium dynamics, as measured recently by other researchers. It appears that rapid motility in dendritic spines increases the efficiency of calcium conduction to the dendrite and speeds up the emptying of the spine. This could play a major role in the induction of synaptic plasticity. A prediction of the model is that alteration of spine motility will modify the time course of calcium in the dendritic spine and could be tested experimentally.

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