Effects of selected neuroactive chemicals on calcium transporting systems in rat cerebellum and on survival of cerebellar granule cells.

This investigation examined the relationship between alteration of Ca(2+)-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 Ca(2+)-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 Ca(2+)-ATPase 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 (microM) 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 Ca(2+)-ATPase activity in a concentration-dependent manner with IC50 values of 62.5, > 400, and 246.9 microM, indicating an effect on the Ca(2+)-extrusion process. Al increased Ca(2+)-ATPase activity (EC50 = 833 microM). Although NMDA did not inhibit Ca(2+)-transport systems, it was cytotoxic at 250 microM and higher concentrations after 2 hr of exposure. Similarly, CPZ was cytotoxic at concentrations of 25 and 10 microM after 4 hr exposure. However, PER, DEL, and Al were not cytotoxic at any concentration up to 500 microM. Of all the chemicals tested, CPZ was the most potent in inhibiting Ca(2+)-transporting systems and was also cytotoxic.(ABSTRACT TRUNCATED AT 250 WORDS)