Effect of lead on the biological activity of calmodulin in rat brain

In the present investigation, we observed that lead in vitro activates calmodulin at lower concentrations, and the maximum activation was observed at 30 microM concentration. In vivo lead exposure (50 mg/kg body weight, intragastrically) for a period of 8 weeks also stimulated the activity of calmodulin by 45%. The addition of trifluoperazine resulted in partially inhibiting the lead-stimulated calmodulin activity, whereas the calcium-stimulated calmodulin activity was completely inhibited by trifluoperazine. Studies with purified calmodulin from the brain of control and lead-treated animals indicate that approximately 4 mole of calcium was present bound/mole of calmodulin in control animals and this fraction was reduced in lead-treated animals to approximately 3 mole of calcium/mole of calmodulin. Lead distribution revealed that approximately 68% of the total lead present was bound to calmodulin and the remaining 32% present was bound to non-calmodulin binding sites following lead exposure. These results indicate that in vivo lead exposure is able to displace and mimic the action of calcium and this may constitute a molecular mechanism of lead neurotoxicity.