LOW-LEVEL LEAD-EXPOSURE IN CULTURED ASTROGLIA - IDENTIFICATION OF CELLULAR TARGETS WITH VITAL FLUORESCENT-PROBES

The effects of lead (0.0, 0. 1, or 1 muM) on subcellular sites in prim ary astroglial cultures were quantitated with the use of vital fluores cent probes (fluorescence bioassays). Evaluation of cellular glutathio ne levels with monochlorobimane revealed a reduction in glutathione co ntent after only 7 hr of Pb treatment to 77 and 82% of control values for 0.1 and 1.0 muM Pb, respectively. A further decrease in intracellu lar glutathione levels (to 74 and 56% of control values, respectively) was observed after 24 hr. Glutathione content returned to control lev els by 48 hr, and exceeded control levels after 6 days (122 and 159% o f control values) and 9 days (135 and 154% of control values) of lead treatment. Whereas glutathione has been shown by others to protect tar get organs from metal toxicity, these findings suggest a compensatory response by astroglia to the effects of Pb. Alterations in astroglial mitochondrial membrane potential were measured with the use of rhodami ne 123. The membrane potential-dependent partitioning of rhodamine 123 was reduced following 14 days of Pb exposure (0. 1 or 1.0 muM) to 75% of control value, indicating that Pb may act to dissipate the electro chemical gradient in astroglial mitochondria. Carboxyfluorescein diace tate was used to evaluate gap junctional intercellular communication ( GJIC) between astroglia by fluorescence recovery after photobleaching. No difference between control and low-level Pb treated astroglia was found. Our results indicate that a Pb-stimulated increase in astroglia l glutathione occurs after a lag period during which levels are decrea sed. Also Pb exerts an injurious effect to the mitochondrial membrane (as indicated by a reduction in its ability to partition rhodamine 123 ) at dosages that have no effect on GJIC This study provides evidence for a protective mechanism in brain cells that take up and store Pb in tracellularly. A period of vulnerability is also evident during which the cell may undergo molecular injury. (C) 1993 Intox Press, Inc.