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

Biophys J. 1997 Mar;72(3):1458-71. doi: 10.1016/S0006-3495(97)78792-7.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials*
  • Animals
  • Animals, Newborn
  • Brain Stem / physiology*
  • Calcium / physiology*
  • Fluorescent Dyes
  • Fura-2
  • In Vitro Techniques
  • Kinetics
  • Mathematics
  • Membrane Potentials
  • Microscopy, Fluorescence
  • Models, Neurological
  • Models, Theoretical
  • Patch-Clamp Techniques
  • Presynaptic Terminals / physiology*
  • Rats
  • Rats, Wistar
  • Tetrodotoxin / pharmacology


  • Fluorescent Dyes
  • Tetrodotoxin
  • Calcium
  • Fura-2