Serum Calmodulin Activity in Male Lead-exposed Workers
Serum calmodulin (CaM) activity was studied in 75 lead-exposed and 21 non-exposed male workers. The lead-exposed workers were divided into groups with low blood lead (BPb < 50 µg/dL) and high blood lead (BPb>/=50 µg/dL). The concentrations of lead, calcium, magnesium, copper, zinc, and free erythrocytic protoporphyrin (FEP) in blood were determined. Serum samples were heated in a water bath (100 degrees C) for 3 minutes and centrifuged for 15 minutes at 4 degrees C (18,000 x g). The supernatants obtained were used to measure CaM activity. The results showed that: 1) Average blood lead concentrations in workers with both low and high levels of exposure were significantly higher than those in controls (p < 0.05). 2) Serum CaM activity in the high-exposure group (31.09 +/- 7.84 µg/dL) was significantly lower than that in controls (78.11 +/- 15.13 µg/dL, p < 0.05). The biological threshold of BPb inhibition of CaM activity was less than 50 µg/dL. 3) Multiple correlation analysis showed a negative dose-response relationship between BPb and CaM activity. The stepwise regression procedure indicated that lead had negative, and calcium and magnesium positive, effects on serum CaM activity. The regression equation was Y = 66.1383 - 1.0857 X&inf1; + 2.9676 X&inf2; + 5.2222 X&inf3; (Y:CaM; X&inf1;:Pb; X&inf2;: Ca; X&inf3;:Mg). These results of the first such study carried out in male lead-exposed workers suggest that lead can inhibit CaM activity in humans.
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