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J Neurophysiol 88: 2172-2176, 2002;
0022-3077/02 $5.00
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The Journal of Neurophysiology Vol. 88 No. 4 October 2002, pp. 2172-2176
Copyright ©2002 by the American Physiological Society

RAPID COMMUNICATION

Inter-Bouton Variability of Synaptic Strength Correlates With Heterogeneity of Presynaptic Ca2+ Signals

Sergei Kirischuk and Rosemarie Grantyn

Developmental Physiology, Johannes Müller Institute of Physiology, Humboldt University Medical School (Charité), 10117 Berlin, Germany

Kirischuk, Sergei and Rosemarie Grantyn. Inter-Bouton Variability of Synaptic Strength Correlates With Heterogeneity of Presynaptic Ca2+ Signals. J. Neurophysiol. 88: 2172-2176, 2002. The elevation of presynaptic calcium concentration is a crucial step in excitation-secretion coupling. However, the amplitudes of action-potential-induced presynaptic calcium transients can display high variability among different terminals. The aim of this study was to clarify whether, at individual boutons, synaptic strength correlates with the average amplitude of presynaptic calcium transients. Low-density collicular cultures were loaded with the calcium indicator Oregon Green bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) 1. Action potentials were blocked with tetrodotoxin. Presynaptic terminals were identified with FM4-64, a use-dependent vesicle marker. Presynaptic calcium influx was elicited by a focal electrical stimulation of single boutons. Whole cell patch-clamp and calcium imaging techniques were used to record GABAergic evoked inhibitory postsynaptic currents (eIPSCs) and presynaptic fluorescence changes in the stimulated terminal. To make the eIPSCs from different boutons comparable, they were normalized to the mean value of miniature IPSCs (mIPSCs) of the postsynaptic cell. Records from 47 boutons showed that eIPSCs varied between 0.5 and 3.0 and presynaptic calcium transients varied between 0.1 and 1.3. However, there was a strong correlation between the mean amplitudes of eIPSCs and presynaptic calcium responses. The eIPSC-[Ca2+]pre relationship allows to use the amplitudes of presynaptic calcium transients as an indicator of release efficacy and, in a set of contacts made by one axon, to predict the relative impact of individual terminals.




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S. Kirischuk and R. Grantyn
Intraterminal Ca2+ concentration and asynchronous transmitter release at single GABAergic boutons in rat collicular cultures
J. Physiol., May 1, 2003; 548(3): 753 - 764.
[Abstract] [Full Text] [PDF]


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