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Biophys J, March 2000, p. 1119-1125, Vol. 78, No. 3

and
*Unite de Neurocybernetique cellulaire, CNRS/UPR 9041, 13009 Marseille, France, and
Laboratory of Biophysics and
Bioelectronics, Dniepropetrovsk State University, 320625 Dniepropetrovsk, Ukraine
In a model of a single synapse with a circular contact
zone and a single concentric zone containing receptor-gated channels, we studied the dependence of the synaptic current on the synaptic cleft
width and on the relative size of the receptor zone. During synaptic
excitation, the extracellular current entered the cleft and flowed into
the postsynaptic cell through receptor channels distributed
homogeneously over the receptor zone. The membrane potential and
channel currents were smaller toward the cleft center if compared to
the cleft edges. This radial gradient was due to the voltage drop
produced by the synaptic current on the cleft resistance. The total
synaptic current conducted by the same number of open channels was
sensitive to changes in the receptor zone radius and the cleft width.
We conclude that synaptic geometry may affect synaptic currents by
defining the volume resistor of the cleft. The in-series connection of
the resistances of the intracleft medium and the receptor channels
plays the role of the synaptic voltage divider. This voltage dividing
effect should be taken into account when the conductance of single
channels or synaptic contacts is estimated from experimental
measurements of voltage-current relationships.
Biophys J, March 2000, p. 1119-1125, Vol. 78, No. 3
© 2000 by the Biophysical Society 0006-3495/00/03/1119/07 $2.00
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