Adenosine-5’-triphosphate (ATP), which is known to play an important role in intracellular energy transfer, also functions extracellularlly as a chemical transmitter in purinergic signal transmission in neurons and endocrine cells. ATP is stored in secretory vesicles and subsequently exocytosed to stimulate various purinergic responses including those of autonomic functions, pain and mechanosensory transduction, neural-glial interactions, as well as platelet aggregation. Solute carrier family 17 (SLC17) has been originally classified as the vesicular glutamate transporter family, but SLC17A9 isoform2/VNUT may play a role in the vesicular storage of ATP and other nucleotides in secretory vesicles such as adrenal chromaffin granules and synaptic vesicles.