There are two classes of glutamate transporters; the excitatory amino acid transporters (EAATs) which depend on an electrochemical gradient of Na+ ions and vesicular glutamate transporters (VGLUTs) which don't. Together, these transporters uptake and release glutamate to mediate this neurotransmitter's excitatory signal and are part of the glutamate-gluatamine cycle.
Three members of the SLC17A gene family (7, 6 and 8) encode VGLUTs 1-3 respectively (Ni et al. 1996, Takamori et al. 2001, Takamori et al. 2002 respectively). VGLUT1 (brain-specific Na+-dependent phopshate transporter, BNPI) and VGLUT2 (differentiation-associated Na+-dependent phosphate transporter, DNPI) were identified first and originally characterized as phosphate transporters. However, they are localized to synaptic vesicles, not the plasma membrane (like EAATs) and transport the organic anion glutamate into synaptic vesicles. This uptake is thought to be coupled to the proton electrochemical gradient generated by a vacuolar type H+-ATPase. They are all expressed in the CNS in neuron-rich areas but VGLUT3 is also expressed on astrocytes and in liver and kidney.