The expression of vesicular glutamate transporters defines two classes of excitatory synapse

The quantal release of glutamate depends on its transport into synaptic ves icles. Recent work has shown that a protein previously implicated in the up take of inorganic phosphate across the plasma membrane catalyzes glutamate uptake by synaptic vesicles. However, only a subset of glutamate neurons ex presses this vesicular glutamate transporter (VGLUT1). We now report that e xcitatory neurons lacking VGLUT1 express a closely related protein that has also been implicated in phosphate transport. Like VGLUT1, this protein loc alizes to synaptic vesicles and functions as a vesicular glutamate transpor ter (VGLUT2). The complementary expression of VGLUT1 and 2 defines two dist inct classes of excitatory synapse.