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

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.