Age-dependent effects of Aroclor 1254 R on calcium uptake by subcellular organelles in selected brain regions of rats

Abstract

Earlier reports from our laboratory have indicated that polychlorinated biphenyls (PCBs) affect signal transduction mechanisms in brain, including Ca 2+ homeostasis, phosphoinositol hydrolysis, and protein kinase C (PKC) translocation in mature neurons and adult brain homogenate preparations. Present studies were designed to investigate whether there were any brain region-, gender-, or age-dependent effects of PCBs on 45Ca 2+-uptake by two subcellular organelles, microsomes and mitochondria. We have studied in vitro effects of a widely studied commercial PCB mixture, Aroclor 1254 R, on 45Ca 2+-uptake by microsomes and mitochondria in cerebellum, frontal cortex and hippocampus of postnatal day (PND) 7, 21, and 90–120 (adult) male and female Long–Evans (LE)-rats. In general, microsomal and mitochondrial 45Ca 2+-uptake in selected brain regions increased with age; PND 7<PND 21≤adults. Among three brain regions, hippocampus had relatively lower microsomal 45Ca 2+-uptake than cerebellum and frontal cortex throughout the development. Mitochondrial 45Ca 2+-uptake was comparable in three brain regions of PND 7 and adult animals, but in PND 21 rats, the cerebellum had much higher activity than frontal cortex and hippocampus. No gender-related differences were seen in 45Ca 2+-uptake by either microsomes or mitochondria in selected brain regions throughout development. Inhibition of 45Ca 2+-uptake by Aroclor 1254 in a concentration-dependent manner was observed throughout the study. However, the degree of inhibition of microsomal 45Ca 2+-uptake in these brain regions by Aroclor 1254 increased with age, PND 7<PND 21≤adults (IC 50s=21–34, 8–20 and 10–14 μM, respectively). Brain region-specific differential sensitivity to Aroclor 1254 on the inhibition of microsomal 45Ca 2+-uptake was not seen in PND 7 and adult animals but in PND 21 rats, hippocampus was more sensitive than the other selected brain regions. There were no age-, gender- or brain region-specific differential effects of Aroclor 1254 on mitochondrial 45Ca 2+-uptake. These results indicate that a commercial PCB mixture, Aroclor 1254, inhibited 45Ca 2+-uptake by both microsomes and mitochondria uniformly in selected brain regions of males and females during development. However, the inhibition of microsomal 45Ca 2+-uptake by Aroclor 1254 increased with age. The age- and gender-related differential sensitivity to Aroclor 1254 may be attributed to the changes in calcium homeostasis in various brain regions during development.