Biochemistry and Molecular Biology of the Vesicular Monoamine Transporter from Chromaffin Granules

Abstract

Prior to secretion, monoamines (catecholamines, serotonin, histamine) are concentrated from the cytoplasm into vesicles by vesicular monoamine transporters (VMAT). These transporters also carry non-physiological compounds, e.g. the neurotoxin methyl-4-phenylpyridinium. VMAT acts as an electrogenic antiporter (exchanger) of protons and monoamines, using a proton electrochemical gradient. Vesicular transport is inhibited by specific ligands, including tetrabenazine, ketanserin and reserpine. The mechanism of transport and the biochemistry of VMAT have been analyzed with the help of these tools, using mainly the chromaffin granules from bovine adrenal glands as a source of transporter. Although biochemical studies did not suggest a multiplicity of VMATs, two homologous but distinct VMAT genes have recently been cloned from rat, bovine and human adrenal glands. The VMAT proteins are predicted to possess 12 transmembrane segments, with both extremities lying on the cytoplasmic side. They possess N-glycosylation sites in a putative luminal loop and phosphorylation sites in cytoplasmic domains. In rat, VMAT1 is expressed in the adrenal gland whereas VMAT2 is expressed in the brain. In contrast, we found that the bovine adrenal gland expressed both VMAT1 and VMAT2. VMAT2 corresponds to the major transporter of chromaffin granules, as shown by partial peptidic sequences of the purified protein and by a pharmacological analysis of the transport obtained in transfected COS cells (COS cells are monkey kidney cells possessing the ability to replicate SV-40-origin-containing plasmids). We discuss the possibility that VMAT1 may be specifically addressed to large secretory granules vesicles, whereas VMAT2 may also be addressed to small synaptic vesicles; species differences would then reflect the distinct physiological roles of the small synaptic vesicles in the adrenal gland.

Syrosingopine sensitizes cancer cells to killing by metformin

“…S1B). Both drugs inhibit the vesicular monoamine transporters (VMAT1 and VMAT2) to prevent sequestration of monoamines into their storage granule, thus depleting catecholamine stores (33,34). Syrosingopine is less potent than reserpine, with consequently weaker antihypertensive activity (35,36).…”

Characterization of a Series of 3-Amino-2-phenylpropene Derivatives as Novel Bovine Chromaffin Vesicular Monoamine Transporter Inhibitors

“…[7][8][9] However, VMAT2 appears to be the major transporter in chromaffin granules of the bovine adrenal medulla. [7][8][9][10] Catecholamines and histamines are shown to exhibit 3-and 30-fold more affinity, respectively, toward VMAT2 in comparison to VMAT1. 7 Reserpine and ketanserin are slightly more potent inhibitors of VMAT2, while tetrabenazine is a specific inhibitor for VMAT2.…”

“…[1][2][3][4] In addition, a large number of illicit drugs and neurotoxins are proposed to exert their neuropharmacological and toxic effects, at least partly, through interference with the physiological functions of VMATs. [6][7]10,[12][13][14][15][16][17][18][19] Despite the physiological significance, the molecular mechanisms related to the biochemical functions of VMATs are still poorly understood. 20 Therefore, it is a significant goal to develop specific probes, which could be used in the structurefunction and mechanistic studies of VMATs.…”

Differential Expression of Secretogranins II and III in Canine Adrenal Chromaffin Cells and Pheochromocytomas

“…50,[64][65][66] In mammals, there are two subtypes of VMATs, VMAT1 and VMAT2, and they transport and store synthesized monoamines in vesicles in preparation for exocytotic release. 38,49,67,68 VMAT1 is predominantly localized in the membranes of core vesicles of various neuroendocrine cells, whereas VMAT2 is mainly localized in the membranes of synaptic vesicles of monoaminergic nerve endings in the central nervous system and sympathetic nervous system and is also found in the dense-core vesicles of chromaffin cells in the adrenal medulla. 66 In rat adrenal chromaffin cells, VMAT2 colocalizes with tyrosine hydroxylase but not with phenylethanolamine N-methyltransferase (PNMT), suggesting that its expression is in noradrenaline-producing cells.…”

“…The packaging of the monoamine transmitter into dense-core vesicles is mediated by specific transporters that are localized on the vesicular membrane, termed vesicular monoamine transporters 1 and 2 (VMAT1 and VMAT2). [38][39][40] The essential differences between both SgII and SgIII in adrenal chromaffin cells have not been fully evaluated. In this study, we evaluated the expression of SgII and SgIII in the normal canine adrenal medulla and utilized immunohistochemistry to compare their expression patterns.…”