PREFERENTIAL LOCALIZATION OF A VESICULAR MONOAMINE TRANSPORTER TO DENSE CORE VESICLES IN PC12 CELLS

Neurons and endocrine cells have two types of secretory vesicle that u ndergo regulated exocytosis. Large dense core vesicles (LDCVs) store n eural peptides whereas small dear synaptic vesicles store classical ne urotransmitters such as acetylcholine, gamma-aminobutyric acid (GABA), glycine, and glutamate. However, monoamines differ from other classic al transmitters and have been reported to appear in both LDCVs and sma ller vesicles. To localize the transporter that packages monoamines in to secretory vesicles, we have raised antibodies to a COOH-terminal se quence from the vesicular amine transporter expressed in the adrenal g land (VMAT1). Like synaptic vesicle proteins, the transporter occurs i n endosomes of transfected CHO cells, accounting for the observed vesi cular transport activity. In rat pheochromocytoma PC12 cells, the tran sporter occurs principally in LDCVs by both immunofluorescence and den sity gradient centrifugation. Synaptic-like microvesicles in PC12 cell s contain relatively little VMAT1. The results appear to account for t he storage of monoamines by LDCVs in the adrenal medulla and indicate that VMAT1 provides a novel membrane protein marker unique to LDCVs.