The In vitro effects on acetylcholinesterase activity of marine medaka(Oryzias javanicus) as a test species by Diazinon and Chlorpyrifos

Abstract

Cholinesterases (ChEs) are a group of enzymes whose main function appears to be to hydrolyzeacetylcholine after it has functioned as a neuro-transmitter. They are inhibited by two main groups of pesticides, the organophosphatesand the carbamates, which combine covalently with specific amino-acid residues to inactivate the enzyme(s). During the 1990’s there was a resurgence of interest in the use of ChE as a \\\\\\\\\\\\\\\\'biomarker\\\\\\\\\\\\\\\\' as evidence accumulated that ChE activity in fish was inhibited at sites not obviously contaminated by organophosphate or carbamate pesticides (e.g., Galgani et al., 1992; Payne et al., 1996), and although the chemical cause of such inhibition is still unidentified, ChE is being used as a bioassay to identify potentially contaminated sites which can be examined in more detail using the approaches of analytical chemistry (e.g., Kirby et al., 2000). In this study, therefore, in vitro studies were conducted using the head PMS of marine medaka (Oryzias javanicus) to examine the effects of two pesticides, diazinon and chlorpyrifos. Marine medeka was selected due to its short life cycle and its potential as an indicator of marine environmental conditions. The results obtained suggest that AChE was relatively insensitive to both chlorpyrifos and diazinon in terms of IC50; kinetic analyses suggested that the inhibition was probably non-compentitive.