Manganese Uptake and Efflux in Cultured Rat Astrocytes

Abstract

Abstract: 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 highaffinity transport system for Mn 2+. Saturation kinetics are clearly indicated by both l/s versus l/s plots (Km= 0.30 ± 0.03 μMM; Vmax= 0.30 ± 0.02 nmol/mg of protein/min) and plots of v versus [s]. Several divalent cations (Co 2, Zn 2+, and Pb 2+) failed to inhibit the initial rate of 54 Mn 2+ uptake. In contrast, extracellular Ca 2+ at 10 μM decreased 54 Mn 2+ uptake. Exchange with extracellular Mn 2+ was not obligatory for the efflux of 54 Mn 2+ into extracellular medium because efflux occurred into Mn 2+‐free extracellular medium, but efflux of 54 Mn 2+ was enhanced when astrocytes were equilibrated in the presence of unlabeled Mn 2+. Efflux of 54 Mn 2+ 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 54 Mn 2+ transported extracellularly, and 37.2 ± 1.2% of preloaded 54 Mn 2+ 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.