Effects of chronic low-level lead exposure on mRNA expression, ADP-ribosylation and photoaffinity labeling with [α 32P]guanine triphosphate-γ-azidoanilide of GTP-binding proteins in neurons isolated from the brain of neonatal and adult rats

Abstract

The effects of chronic lead exposure on mRNA expression, ADP-ribosylation and photoaffinity labeling with [α 32P]guanine triphosphate-γ-azidoanilide ([ 32P]GTP-A) of α i or α s subunit of G protein were investigated in neurons isolated from the brain of neonatal and adult rats exposed to lead acetate or sodium acetate (for control). Rats were exposed by oral feeding for 10 days or 20 weeks to a low level of lead acetate or sodium acetate. The exposure started either prenatally or at an adult age. The expression of α i -mRNA in neurons obtained from the brain of control neonatal rats was significantly higher than that of the expression in samples obtained from the brain of control adult rats or the brain of rats exposed to lead at an adult age. The expression of α i -mRNA in neurons obtained from the brain of control neonatal rats, lead-exposed neonatal rats and adult rats prenatally exposed to lead did not differ significantly. Chronic lead exposure did not affect the expression of α s -mRNA in neurons obtained from the brain of neonatal and adult rats. The ADP-ribosylation or the photoaffinity labeling with [ 32 P]GTP-A of α i or α s , subunits reflected the developmental pattern of the expression of α i , or α s -mRNA. The incorporation of radioactivity in α i -subunit obtained from the brain of control neonatal rats, lead-exposed neonatal rats and rats prenatally exposed to lead was greater than the incorporation in α i-subunit obtained from the brain of control adult rats or rats exposed to lead at an adult age. The incorporation of radioactivity did not differ significantly in α s -subunits obtained from control or lead-exposed neonatal and adult rats. These observations indicate that (1) the mRNA expression, ADP-ribosylation and photoaffinity labeling with [ 32 P]GTP-A of α i- subunit decrease, whereas the mRNA expression, ADP-ribosylation and photoaffinity labeling with [ 32 P]GTP-A of α s- subunit do not change as animals age after postnatal day 10, (2) chronic prenatal lead exposure delays the age-dependent decrease in mRNA expression, ADP-ribosylation and photoaffinity labeling of α i subunit, and (3) chronic adult exposure does not cause these changes.