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Calcium Dynamics associated with a single action potential in a CNS presynaptic terminal

MPG-Autoren
http://pubman.mpdl.mpg.de/cone/persons/resource/persons93373

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

http://pubman.mpdl.mpg.de/cone/persons/resource/persons92286

Borst,  J. Gerard G.
Department of Cell Physiology, Max Planck Institute for Medical Research, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons95089

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

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Zitation

Helmchen, F., Borst, J. G. G., & Sakmann, B. (1997). Calcium Dynamics associated with a single action potential in a CNS presynaptic terminal. Biophysical Journal, 72(3), 1458-1471. doi:10.1016/S0006-3495(97)78792-7.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-0024-C0E2-D
Zusammenfassung
Calcium dynamics associated with a single action potential were studied quantitatively in the calyx of Held, a large presynaptic terminal in the rat brainstem. Terminals were loaded with different concentrations of high- or low-affinity CA2+ indicators via patch pipettes. Spatially averaged CA2+ signals were measured fluorometrically and analyzed on the basis of a single compartment model. A single action potential led to a total CA2+ influx of 0.8-1 pC. The accessible volume of the terminal was about 0.4 pl; thus the total calcium concentration increased by 10-13 microM. The Ca(2+)-binding ratio of the endogenous buffer was about 40, as estimated from the competition with Fura-2, indicating that 2.5% of the total calcium remained free. This is consistent with the peak increase in free calcium concentration of about 400 nM, which was measured directly with MagFura-2. The decay of the [CA2+]i transients was fast, with time constants of 100 ms at 23 degrees C and 45 ms at 35 degrees C, indicating CA2+ extrusion rates of 400 and 900 s-1, respectively. The combination of the relatively low endogenous Ca(2+)-binding ratio and the high rate of CA2+ extrusion provides an efficient mechanism for rapidly removing the large CA2+ load of the terminal evoked by an action potential