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Competitive calcium binding: implications for dendritic calcium signaling

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Markram,  Henry
Department of Cell Physiology, Max Planck Institute for Medical Research, Max Planck Society;

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Roth,  Arnd
Department of Cell Physiology, Max Planck Institute for Medical Research, Max Planck Society;

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Helmchen,  Fritjof
Department of Cell Physiology, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Markram, H., Roth, A., & Helmchen, F. (1998). Competitive calcium binding: implications for dendritic calcium signaling. Journal of Computational Neuroscience, 5(3), 331-348. doi: 10.1023/A:1008891229546.


Cite as: http://hdl.handle.net/11858/00-001M-0000-002B-98F3-1
Abstract
Action potentials evoke calcium transients in dendrites of neocortical pyramidal neurons with time constants of < 100 ms at physiological temperature. This time period may not be sufficient for inflowing calcium ions to equilibrate with all present Ca2+-binding molecules. We therefore explored nonequilibrium dynamics of Ca2+ binding to numerous Ca2+ reaction partners within a dendritelike compartment using numerical simulations. After a brief Ca2+ influx, the reaction partner with the fastest Ca2+ binding kinetics initially binds more Ca2+ than predicted from chemical equilibrium, while companion reaction partners bind less. This difference is consolidated and may result in bypassing of slow reaction partners if a Ca2+ clearance mechanism is active. On the other hand, slower reaction partners effectively bind Ca2+ during repetitive calcium current pulses or during slower Ca2+ influx. Nonequilibrium Ca2+ distribution can further be enhanced through strategic placement of the reaction partners within the compartment. Using the Ca2+ buffer EGTA as a competitor of fluo-3, we demonstrate competitive Ca2+ binding within dendrites experimentally. Nonequilibrium calcium dynamics is proposed as a potential mechanism for differential and conditional activation of intradendritic targets.