Szegletes_1995_Pestic.Biochem.Physiol_52_71

The activity and molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) were characterized in the heart and skeletal muscle of carp (Cyprinus carpio L.) exposed to 2 mg/liter of the insecticide methidathion (MD; S-2,3-dihydro-5-methoxy-2-oxo-1,3,4-thiodiazol-3-yl-methyl-O,O-dimethyl phosphodithioate) for 5 days at a water temperature of 12 +/- 1degC. The specific activity of the heart AChE (4.78 +/- 2.14 10-2 U/mg protein) was higher than that of the muscle AChE (2.53 +/- 0.75 10-2 U/mg protein) in control carp. The solubility properties and molecular forms of the AChE in the two tissues were studied by extraction in high-salt medium (1 and 0.4 M NaCl) with and without Triton X-100. The ratio of membrane-bound to salt-soluble forms of AChE was higher in the muscle than in the heart. Velocity sedimentation centrifugation revealed that the skeletal muscle and the heart contained three molecular forms: G4, A4, and A12. After the in vivo exposure of fish to MD, the AChE activity decreased significantly (77-92%) in the tissues investigated. Furthermore, the relative distribution of the AChE molecular forms differed somewhat from that in the control fish. Form Gl became detectable after the treatment, but could not be measured in the control tissues. The proportions of the other forms decreased by a few percentages. The accumulation of MD was studied in seven organs: the brain, heart, intestine, kidney, liver, muscle, and roe. The liver and roe had the highest MD contents, and the heart and muscle had the lowest. This study shows the MD not only blocks the activity of AChE, but also modifies the distribution of its molecular forms.