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Ca2+ buffering and action potential-evoked Ca2+ signaling in dendrites of pyramidal neurons

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

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Sakmann,  Bert
Department of Cell Physiology, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Helmchen, F., Imoto, K., & Sakmann, B. (1996). Ca2+ buffering and action potential-evoked Ca2+ signaling in dendrites of pyramidal neurons. Biophysical Journal, 70, 1069-1081.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0024-42E9-9
Abstract
The effect of the fluorescent Ca2+ indicator dye Fura-2 on Ca2+ dynamics was studied in proximal apical dendrites of neocortical layer V and hippocampal CA1 pyramidal neurons in rat brain slices using somatic whole-cell recording and a charge-coupled device camera. A single action potential evoked a transient increase of intradendritic calcium concentration ([Ca2+]i) that was reduced in size and prolonged when the Fura-2 concentration was increased from 20 to 250 microM. Extrapolation to zero Fura-2 concentration suggests that "physiological" transients at 37 degrees C have large amplitudes (150–300 nM) and fast decays (time constant < 100 ms). Assuming a homogeneous compartment model for the dendrite, 0.5–1% of the total Ca2+ entering during an action potential was estimated to remain free. Washout of cytoplasmic Ca2+ buffers was not detectable, suggesting that they are relatively immobile. During trains of action potentials, [Ca2+]i increased and rapidly reached a steady state (time constant < 200 ms), fluctuating around a plateau level which depended linearly on the action potential frequency. Thus, the mean dendritic [Ca2+]i encodes the action potential frequency during physiological patterns of electrical activity and may regulate Ca(2+)-dependent dendritic functions in an activity-dependent way.