Effect of carbon tetrachloride on inositol 1,4,5-trisphosphate dependent and independent regulation of rat brain microsomal Ca²⁺ flux

Carbon tetrachloride (CCl₄) is a highly toxic industrial solvent with pronounced effects of the liver and brain. CCl₄ is enzymatically cleaved to produce free radicals which attack membrane components, including proteins. Earlier indicated that CCl₄ affects Ca²⁺-regulated events in the brain. Hence, the present study was initiated to determine whether CCl₄ affects inositol 1,4,5-triphosphate (IP₃) receptor binding, free-Ca²⁺ movements across the microsomal membrane and protein kinase C (PKC) activity in rat brain, since IP₃₊ Ca²⁺ and PKC are known to be involved in signal transduction. [³H]IP₃ binding, free-Ca²⁺ movements and ⁴⁵C²⁺ uptake were determined using rat brain microsomes and PKV activitity was determined in the cytosolic fraction. CCl₄ in vitro decreased [³H]IP₃ binding to microsomes. IP₃ mediated Ca²⁺ release from microsomes was inhibited and also the re-uptake of IP₃-released Ca²⁺ into microsomes was decreased in the presence of CCl₄. CCl₄ at concentrations < 2 μM independentl;y released Ca²⁺ from microsomes. Uptake of total Ca²⁺ into microsomes was inhibited by CCl₄ as observed with ⁴⁵Ca²⁺-uptake studies. CCl₄ at 1 μM inhibited PKC activity by 50%. Thus, perturbations in the binding of IP₃ to its receptor sites, changes in the Ca²⁺ flux across the microsomal membrane and modulation of PKC activity by CCl₄ in vitro suggested that CCl₄ may exert neurotoxicity by altering signaltransduction pathways.