Manganese uptake and efflux in cultured rat astrocytes.
Astrocytes play a central role in manganese (Mn) regulation in the CNS. Using primary astrocyte cultures from neonatal rat brains, these studies demonstrate a specific high-affinity transport system for Mn2+. Saturation kinetics are clearly indicated by both 1/v versus 1/s plots (Km = 0.30 +/- 0.03 microM; Vmax = 0.30 +/- 0.02 nmol/mg of protein/min) and plots of v versus [s]. Several divalent cations (Co2+, Zn2+, and Pb2+) failed to inhibit the initial rate of 54Mn2+ uptake. In contrast, extracellular Ca2+ at 10 microM decreased 54Mn2+ uptake. Exchange with extracellular Mn2+ was not obligatory for the efflux of 54Mn2+ into extracellular medium because efflux occurred into Mn(2+)-free extracellular medium, but efflux of 54Mn2+ was enhanced when astrocytes were equilibrated in the presence of unlabeled Mn2+. Efflux of 54Mn2+ was biphasic with both a rapid and a slow component. Efflux was most rapid during the first 10 min of incubation, with 27.5 +/- 2.2% of 54Mn2+ transported extracellularly, and 37.2 +/- 1.2% of preloaded 54Mn2+ was retained by the astrocytes at 120 min. These studies show, for the first time, that mammalian astrocytes can transport Mn via a specific transport system.
Aschner
M
M
Department of Pharmacology and Toxicology, Albany Medical College, New York 12208.
Gannon
M
M
Kimelberg
H K
HK
D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003470:Culture Media; D005110:Extracellular Space / Q000378:metabolism; D008345:Manganese / Q000493:pharmacokinetics*; D009994:Osmolar Concentration; D051381:Rats; D012964:Sodium / Q000494:pharmacology
D003470:Culture Media; D008345:Manganese; D012964:Sodium; D002118:Calcium