CADMIUM CHLORIDE (CDCL2)-INDUCED METALLOTHIONEIN (MT) EXPRESSION IN NEONATAL RAT PRIMARY ASTROCYTE CULTURES

Metallothionein (MT) protein and mRNA levels were studied following ex posure of rat neonatal primary astrocyte cultures to cadmium chloride (CdCl2). MT mRNA was probed on Northern blots with a P-32 labeled synt hetic cDNA probe specific for rat MT mRNA. The probe hybridizes to a s ingle mRNA with a size appropriate for MT, approximately 550 bases. Ex pression of MT-I mRNA in astrocyte monolayers exposed to 2 X 10(-6) M CdCl2 for 6 h was increased approximately 5-fold (9.7 fg/mu g total RN A) over MT-I mRNA levels in controls (2 fg/mu g total RNA). MT-I mRNA could also be detected in untreated cells, suggesting constitutive MT expression in these cells. Western-blot analysis revealed a marked inc rease in MT protein levels upon exposure to CdCl2 (1 x 10(-6) M; 96 h) . Consistent with the constitutive expression of MTs both at the mRNA level and protein level, we have also demonstrated a time-dependent in crease in MT-immunoreactivity in astrocytes exposed to CdCl2. The pres ent study suggests that astrocytes constitutively express MTs, and tha t MT-induction by CdCl2 may be an example of a generalized increase in MTs in response to heavy metal exposure, thus protecting astrocytes, and perhaps also indirectly, juxtaposed neurons from the neurotoxic ef fects of heavy metals.