Me. Legare et al., LOW-LEVEL LEAD-EXPOSURE IN CULTURED ASTROGLIA - IDENTIFICATION OF CELLULAR TARGETS WITH VITAL FLUORESCENT-PROBES, Neurotoxicology, 14(2-3), 1993, pp. 267-272
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.