© 1993 Oxford University Press
research-article |
Effects of Selected Neuroactive Chemicals on Calcium Transporting Systems in Rat Cerebellum and on Survival of Cerebellar Granule Cells1,2
*Cellular and Molecular Toxicology Branch, Neurotoxicology Division, Health Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park North Carolina 27711
Division of Intramural Research, National Institute of Environmental Health Sciences, Research Triangle Park North Carolina 27709
Received December 21, 1992; accepted June 18, 1993
This investigation examined the relationship between alteration of Ca2+-transport systems and cytotoxicity in vitro for a number of neuroactive chemicals including environmental pollutants. 45Ca2+ uptake as a measure of Ca2+ sequestration was determined in mitochondria and microsomes isolated from cerebella of adult male Long-Evans hooded rats by differential centrifugation. Ca2+ extrusion, measured as Ca2+-ATPase activity, was determined in synaptosomes prepared by sucrose density gradient. Cytotoxicity (lactate dehydrogenase leakage) was assessed in primary cultures of cerebellar granule cells from 6- to 8-day-old Long-Evans rats. N-Methyl-D-aspartic acid (NMDA) did not alter synaptosomal Ca2+ activity or 45Ca2+ uptake in mitochondria and microsomes. However, chlorpromazine (CPZ), aluminum (Al), permethrin (PER), and deltamethrin (DEL) inhibited Ca2+ sequestration by mitochondria and microsomes. The IC50 values (µM) for CPZ, Al, PER, and DEL were 67.8, 671, 4.2, and 91.2 for mitochondrial 45Ca2+ uptake, and 129.9, 1384, >50, and >200 for microsomal 45Ca2+ uptake, respectively. CPZ, PER, and DEL also inhibited synaptosomal Ca2+-ATPase activity in a concentration-dependent manner with IC50 values of 62.5, >400, and 246.9 µM, indicating an effect on the Ca2+ process. Al increased Ca2+ATPase activity (EC50=833 µM). Although NMDA did not inhibit Ca2+ systems, it was cytotoxic at 250 µM and higher concentrations after 2 hr of exposure. Similarly, CPZ was cytotoxic at concentrations of 25 and 10µ after 4 hr exposure. However, PER, DEL, and Al were not cytotoxic at any concentration up to 500 µM. Of all the chemicals tested, CPZ was the most potent in inhibiting Ca2+ systems and was also cytotoxic. These results indicate that the selected chemicals, all of which are known to alter cellular Ca2+ homeostasis, altered 2+-transporting systems in the cerebellum and exhibited cytotoxicity in cerebellar granule cells to different extents. Cytotoxic potencies of chemicals used in this study can be related to both effects on Ca2+ influx and inhibition of Ca2+ systems.