Changes in synaptosomal pH and rates of oxygen radical formation induced by chlordecone

Abstract

The resting pH of 7.14 +/- 0.02 within rat cortical synaptosomes is elevated in vitro by the insecticide chlordecone, in a dose-dependent manner. Chlordecone also reduces the rate of oxygen radical formation within synaptosomes. Both of these changes can also be demonstrated following in vivo treatment of rats with chlordecone (75 mg/kg body wt). Although chlordecone increases the permeability of the plasma membrane, the increase in pH observed is unlikely to be caused by this, since in vivo administration of chlordecone does not appreciably alter membrane order as evaluated by both a lipophilic probe, and a probe with an ionic segment. Another xenobiotic agent, methyl mercuric chloride, and a free radical generating system, an ascorbic acid-ferrous sulfate mixture, did not modulate synaptosomal pH, although membrane permeability was increased. Other evidence of the ability of synaptosomes to maintain homeostasis was the failure of mitochondrial inhibitors to significantly reduce pH. The drop in synaptosomal pH effected by amiloride, an inhibitor of Na+/H+ exchange, and the transient rise in pH caused by ammonium chloride further suggested that synaptosomes may be a good model in the study of the regulation of intracellular pH. The elevation of cytosolic pH, and depression of oxygen radical formation by chlordecone, may result from both the attenuation of respiratory metabolism and an impaired capacity of the plasma membrane to maintain ionic gradients.

Evaluation of the probe 2',7'-dichlorofluorescin as an indicator of reactive oxygen species formation and oxidative stress

“…In the presence of H202 + Fe2+, EDTA partially prevented the formation of DCF, and surprisingly DETAP AC enhanced DCFH oxidation, in which fluorescence intensity readings actually exceeded the upper limits of detection (Table I). There is no ready explanation for the rapid conversion of DCFH to DCF by DETAP AC in this system, although it has been reported that Fe2+-DE-TAPAC chelates may actually catalyze the formation of ethylene gas from S-methyl 2-ketothiobutyrate, phenol from benzene, and the formation of the hydroxyl spin adduct of 5,5-dimethyl-l-pyrroline N-oxide (27).…”

“…DCFH's lack of specificity toward reactive oxygen species is what makes it pot.entially appealing as a probe in studying toxicological phenomena. Numerous studies exist demonstrating the utility of DCFH as an index of free radical reactions that take place in the living animal following exposure to toxic chemicals (9,(27)(28)(29). Toxicology studies using DCFH have reported the following: (1) significant differences in brain DCF formation rates between vitamin E deficient mice and those provided normal diets (8); (2) significant differences in DCF formation rat.es in brain regions known to be selectively vulnerable to the neurotoxic organometals methylmercury and trimethyltin (9); (3) significant differences in brain DCF formation rates in animals pretreated with deferoxamine prior to exposure to methylmercury (30); (4) significant differences in brain DCF formation rates in animals exposed to toluene, a neurotoxic organic solvent, in contrast to no observable alt.erations in brain DCF formation in animals treated with the structurally related solvent benzene (31).…”