Elevation of cytosolic Ca2+ level in the postsynaptic cell is critical for the induction of many forms of activity-dependent synaptic modulation. Based on our recent evidence that in muscle cells and fibroblasts constitutive exocytosis is increased by elevating cytosolic Ca2+ levels, we hypothesize that Ca(2+)-dependent exocytosis at the postsynaptic site may provide a mechanism for a localized, activity-dependent synaptic modulation.