The existence of a second vesicular glutamate transporter specifies subpopulations of glutamatergic neurons

Before their exocytotic release during stimulation of nerve terminals, nonp eptide neurotransmitters are loaded into synaptic vesicles by specific tran sporters. Recently, a protein initially identified as brain-specific Na+-de pendent inorganic phosphate transporter I (BNPI) has been shown to represen t a vesicular glutamate transporter (VGLUT1). In this study, we investigate d whether a highly homologous "differentiation-associated Na+-dependent ino rganic phosphate transporter" (DNPI) is involved in glutamatergic transmiss ion. Vesicles isolated from BON cells expressing recombinant DNPI accumulat ed L-glutamate with bioenergetical and pharmacological characteristics iden tical to those displayed by VGLUT1 and by brain synaptic vesicles. Moreover , DNPI localized to synaptic vesicles, at synapses exhibiting classical exc itatory features. DNPI thus represents a novel vesicular glutamate transpor ter (VGLUT2). The distributions of each VGLUT transcript in brain were high ly complementary, with only a partial regional and cellular overlap. At the protein level, we could only detect either VGLUT1- or VGLUT2-expressing pr esynaptic boutons. The existence of two VGLUTs thus defines distinct subset s of glutamatergic neurons.