title: High-affinity L-aspartate transporter in prostate epithelial cells that is regulated by testosterone.
abstract: The prostate gland produces and secretes extraordinarily high levels of citrate. Studies with rat ventral prostate (VP) have demonstrated that aspartate can serve as a four-carbon source of oxalacetate in the synthesis of citrate. To achieve this, prostate secretory epithelial cells must contain a transport system for the active uptake of aspartate from circulation. The present studies with VP epithelial cells confirm the existence of a Na(+)-dependent high-affinity L-aspartate transporter. The transporter has an optimal pH approximately 7.5 and is temperature dependent. It appears to be an anionic amino acid transporter capable of transporting L-glutamate but not basic or neutral amino acids. The transporter is inhibited by ATPase inhibitors, thereby indicating its dependency on a Na+ gradient. The characteristics of the high-affinity L-aspartate transporter are consistent with its operation at the basilar membrane for the transport of circulating aspartate into the cell. Castration (24 hr) resulted in a significant decrease in the ability of VP epithelial cells to transport L-aspartate. The administration of testosterone to castrated rats completely restored L-aspartate transport. In addition, in vitro testosterone addition (10(-8) M for 30 min) to isolated prostate epithelial cells markedly increased L-aspartate transport. Both cycloheximide and actinomycin inhibited the testosterone effect. The studies reveal that testosterone is a regulator of this Na(+)-dependent high-affinity L-aspartate transporter. The mechanism of this testosterone effect appears to involve both RNA and protein synthesis. We now have a model system to elucidate this novel effect of testosterone.
authors.affiliation: Department of Physiology, Dental School, University of Maryland, Baltimore 21201.
authors.forename: L
authors.initials: L
authors.lastname: Lao
authors.forename: R B
authors.initials: RB
authors.lastname: Franklin
authors.forename: L C
authors.initials: LC
authors.lastname: Costello
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002478:Cells, Cultured; D004848:Epithelium / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008297:Male; D011467:Prostate / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D013696:Temperature; D013739:Testosterone / Q000494:pharmacology*
chemical_list: D001224:Aspartic Acid; D013739:Testosterone; D012964:Sodium