F-19 NMR-STUDY OF THE EFFECT OF LEAD ON INTRACELLULAR FREE CALCIUM IN HUMAN PLATELETS

Lead has been shown to affect calcium homeostasis. However, there is no prior evidence to indicate an effect of low concentrations of lead in the environment (almost-equal-to 1-mu-M) on the intracellular free Ca2+ concentration in any human tissue. We have investigated the effect of lead on the intracellular free Ca+ concentration of human blood platelets using F-19-NMR and a fluorinated intracellular Ca2+ indicator. We report a basal intracellular free Ca2+ value of 172 +/- 8 nM. Treatment with 1, 5, 10 and 25-mu-M Pb2+ resulted in average increases in intracellular free Ca2+ of 39%, 91%, 135% and 172%, respectively. The percent increase in intracellular free Ca2+ was linearly and positively correlated with the log of Pb2+ concentration. Using atomic absorption spectroscopy, a significant increase in total calcium of approx. 10 nmol/mg protein was found in 25-mu-M Pb2+ treated platelets. This indicates that influx of external Ca2+ contributes to the observed increase in free Ca2+. The results provide an explanation for the previously reported effects of lead on platelet function, and suggest a mechanism for low level lead-induced hypertension.