Stress Modulation of Solute Transport in Choroid

33 The choroid plexus epithelium forms the blood-cerebrospinal fluid barrier and 34 accumulates essential minerals and heavy metals. Choroid plexus is cited as being a ‘sink’ for 35 heavy metals and excess minerals, serving to minimize accumulation of these potentially toxic 36 agents in the brain. Understanding of how low doses of contaminant metals might alter transport 37 of other solutes in choroid plexus is limited. Using primary cultures of epithelial cells isolated 38 from neonatal rat choroid plexus, our objective was to characterize modulation of apical uptake 39 of the model organic cation choline elicited by low concentrations of the contaminant metal 40 cadmium (CdCl2). At 50-1000 nM, cadmium did not directly decrease or increase 30-min apical 41 uptake of 10 μM [H]choline. However, extended exposure to 250-500 nM cadmium increased 42 [H]choline uptake by as much as 75% without marked cytotoxicity. In addition, cadmium 43 induced heat shock protein 70 and heme oxygenase-1 protein expression and markedly induced 44 metallothionein (Mt-1) gene expression. The antioxidant N-acetylcysteine attenuated stimulation 45 of choline uptake and induction of stress proteins. Conversely, an inhibitor of glutathione 46 synthesis L-buthionine-sulfoximine (BSO) enhanced stimulation of choline uptake and induction 47 of stress proteins. Cadmium also activated ERK1/2 MAP kinase. The MEK1 inhibitor PD98059 48 diminished ERK1/2 activation and attenuated stimulation of choline uptake. Furthermore, 49 inhibition of ERK1/2 activation abated stimulation of choline uptake in cells exposed to 50 cadmium with BSO. These data indicate in choroid plexus exposure to low concentrations of 51 cadmium may induce oxidative stress and consequently stimulate apical choline transport 52 through activation of ERK1/2 MAP kinase. 53 54