Effect of tri-o-cresyl phosphate and methamidophos on Ca uptake by brain synaptosomes in hens

The effect of tri-o-cresyl phosphate (TOCP) and methamidophos (MET) on potassium-stimulated ⁴⁵Ca uptake by brain synaptosomes in hens was studied. An in vivo test showed that TOCP increased potassium-stimulated calcium uptake 2 h after its administration, but that verapamil suppressed the enhancement of this calcium uptake. An in vitro test showed that lower concentrations of TOCP stimulated calcium uptake by synaptosomes, but that higher concentrations inhibited the uptake. In contrast, all tested concentrations of MET obviously inhibited calcium uptake; however, since calcium uptake was decreased by the administration of verapamil plus either TOCP or MET, the mechanism by which TOCP affects the voltage-operated calcium channel may be different from that of MET. The disruption of calcium homeostasis may be involved in organophosphate-induced delayed neurotoxicity (OPIDN). Calcium channel blocker may ameliorate OPIDN by maintaining calcium homeostasis in nerve cells.