Table 1.

Definitions of parameters used in the FD model

SymbolDefinition
CaXFConcentration of calcium-bound site XF
CaXDConcentration of calcium-bound siteXD
FFacilitation variable; fraction of available sites activated by a stimulus
DDepression variable; fraction of sites that are release-ready
pRProbability of release; product of the probabilities F and D
F1Initial probability of release
KFAffinity ofCaXF for the release site
KDAffinity ofCaXD for the release site
τFDecay time constant ofCaXF after an action potential
τDDecay time constant ofCaXD after an action potential
ΔFIncremental increase inCaXF after a stimulus
ΔDIncremental increase inCaXD after a stimulus
koBaseline rate of recovery from the refractory state
kmaxMaximal recovery rate from the refractory state
ρFacilitation ratio EPSC2/EPSC1 for closely spaced EPSCs
NTTotal number of release sites
αAverage mEPSC size