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Human erythrocyte membrane Ca(2+)-ATPase during occupational exposure to lead
J U Imah-Harry1, M O Akiibinu, I O Omotosho
1Laboratories for Biomembrane Research and Biotechnology, Department of Biochemistry, College of Medicine, University of Ibadan, Ibadan, Nigeria.
Objective:
Erythrocyte membrane Ca(2+)-ATPase activity was determined in workers occupationally exposed to lead because of the prevalence of elevated blood lead in auto-mobile workers in some urban areas in Nigeria.
Materials And Methods:
Blood lead levels, biochemical profiles, lipid peroxidation, basal and calmodulin-stimulated Ca(2+)-ATPase activities were determined in erythrocytes of different categories of workers occupationally exposed to lead. These subjects were mainly battery chargers (BC), spray painters (SP) and auto mechanics (MC).
Results:
Estimation of erythrocyte Ca(2+)-ATPase activity in the absence of calmodulin (basal activity) in test groups indicated that there were significant reductions in the pump function and this correlated very well with the levels of lead in their blood. Specifically, blood lead levels were of the order: BC (5.5 folds) > SP (4 folds) > MC, although there was no significant difference between the blood lead levels in MC (10.60 +/- 2.55 microgPb2+/dl) and CT (8.51 +/- 4.55 microgPb2+/dl). Similarly, the order of reduction in Ca(2+)-ATPase activity was BC (69.8%) > SP (52.8%) > MC (32.6%). There was significant difference in the values obtained for MC and CT, ATPase activity being lower in MC compared to CT or healthy individuals. In the presence of calmodulin, basal ATPase activity was increased by at least four fold in erythrocytes from healthy subjects (CT) while the basal activity of the enzymes in membranes of BC, SP and MC was enhanced by about one and half times the activity of the pump in membranes from CT. The levels of total serum protein and albumin increased significantly in BC, SP and MC when compared to healthy subjects (CT). C-reactive proteins (C-RP) levels were higher in BC, SP and MC in comparison to CT. The levels of MDA were high in all lead-exposed workers, BC > SP > MC relative to CT. Although, there were significant decreases in the PCV values of all the groups occupationally exposed to lead compared to values obtained for CT, cholesterol level increased significantly only in BC when compared to the other groups.
Conclusion:
These observations are probably due to the integrity of the plasma membrane of these workers and the ability of the heavy metal to compete with Ca2+ in the catalytic cycle and Ca2+ transport mechanism of the pump protein.
