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 on the liver and brain. CCl4 is enzymatically cleav ed to produce free radicals which attack membrane components, includin g proteins. Earlier reports indicated that CCl4 affects Ca2+-regulated events in the brain. Hence, the present study was initiated to determ ine whether CCl4 affects inositol 1,4,5-trisphosphate (IP3) receptor b inding, free-Ca2+ movements across the microsomal membrane and protein kinase C (FKC) activity in rat brain, since IP3, Ca2+ and PKC are kno wn to be involved in signal transduction. [H-3]IP3 binding, free-Ca2movements and Ca-45(2+) uptake were determined using rat brain microso mes and PKC activity was determined in the cytosolic fraction. CCl4 in vitro decreased [H-3]IP3 binding to microsomes. IP3 mediated Ca2+ rel ease from microsomes was inhibited and also the re uptake of IP3-relea sed Ca2+ into microsomes was decreased in the presence of CCl4. CCl4 a t concentrations < 2 mu M independently released Ca2+ from microsomes. Uptake of total Ca2+ into microsomes was inhibited by CCl4 as observe d with Ca-45(2+)-uptake studies. CCl4 at 1 mu M inhibited PKC activity by 50%. Thus, perturbations in the binding of IP3 to its receptor sit es, changes in the Ca2+ flux across the microsomal membrane and modula tion of PKC activity by CCl4 in vitro suggested that CCl4 may exert ne urotoxicity by altering signal transduction pathways.