Organophosphorus compound-induced modification of SH-SY5Y human neuroblastoma mitochondrial transmembrane potential

Organophosphorus (OP) compounds inhibit mitochondrial enzymes, respiration, and ATP generation, in addition to inducing structural changes such as mat rix swelling. This implicates mitochondria as primary subcellular targets f or these compounds. In this study, the health and function of cellular mito chondria following OP compound exposure were assessed by evaluating the mit ochondrial transmembrane potential (Delta Psi(m)). This was done by measuri ng the changes in Delta Psi(m) in SH-SY5Y human neuroblastoma cells incubat ed with the cationic fluorochrome, rhodamine 123 (5 mu g/ml), and the OP co mpounds tri-ortho-tolyl phosphate (TOTP), triphenyl phosphite (TPPi), or pa rathion for 7.5 to 960 minutes. OP compounds (100 mu M to 1 mM) induced sig nificant concentration-dependent mitochondrial hyperpolarization with peak maxima occurring at 60 (TOTP, TPPi) or 120 (parathion) min. Following this, the mitochondrial membranes gradually depolarized. Pretreatment with cyclo sporin A (500 nM, 30 h), a mitochondrial permeability transition pore (PTP) inhibitor, decreased the hyperpolarization. In contrast, 30-h pretreatment with the muscarinic receptor agonist carbachol(1 mM) significantly increas ed Delta Psi(m) and delayed subsequent depolarization. Hyperpolarization an d subsequent depolarization of mitochondrial membranes occurred 16 to 24 h prior to a loss of substrate adhesion or an increase in DNA fragmentation, indicating that mitochondria were a primary target in OP compound-initiated cytotoxicity. (C) 1999 Academic Press.