Enhancement of Zymosan-Induced Respiratory Burst of Rat Neutrophils by Lead in Vitro

Abstract

The effect of Pb²⁺ on serum-treated zymosan (STZ)-induced O₂ consumption of rat peritoneal neutrophils was studied. Pb²⁺ was found to mimic effectively the enhancing action of Ca²⁺ on the O₂ consumption depending on the concentration up to about 80 μM. However, at concentrations over 80 μM, Pb²⁺ inhibited the O₂ consumption. The enhancing effect of Pb²⁺ on the O₂ consumption was further examined using the intracellularly Ca²⁺ -depleted neutrophils. Pb²⁺ also enhanced the O₂ consumption of the Ca²⁺-depleted cells as effectively as Ca²⁺. The Pb²⁺-enhanced O₂ consumption of the Ca²⁺-depleted cells was inhibited by N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) based on its calmodulin antagonistic action. The effect of Pb²⁺ on the activity of activator-deficient 3', 5'-cyclic nucleotide phosphodiesterase (PDE), a calmodulin-dependent enzyme, was examined. Pb²⁺ activated PDE as effectively as Ca²⁺ only in the presence of calmodulin. The Pb²⁺-activated PDE activity was also inhibited by W-7 only in the presence of calmodulin. These results indicated that Pb²⁺ could replace Ca²⁺ in the activation process(es) of the respiratory burst, suggesting a possible involvement of calmodulin in the enhancing mechanism of the O₂ consumption by Pb²⁺.