Table 3.

Effects of addition of EDTA on in vitro inhibition of cholinesterase in neonatal and adult rat heart by chlorpyrifos oxon.

EDTA	Adult	Neonate
0 mM	200 (78–514)	17 (12–25)
2 mM	128 (74–221)	14 (9–24)

Adult and neonatal hearts were minced and frozen at −70°C. Thawed samples were then homogenized in 5 mM HEPES buffer, pH 7.4 in the presence or absence of EDTA (2 mM). Aliquots of homogenates were pre-incubated with a range of chlorpyrifos oxon concentrations for 30 minutes at 37°C. Residual enzyme activity was then measured as described in the Materials and Methods section. Data represent IC₅₀ values (nM) with 95% confidence intervals in parentheses.