Increasing evidence suggest that intracellular calcium mediator proteins may be critical targets for the toxic actions of Pb2+ ions. Recent studies in this laboratory demonstrated that in toxicologically relevant release of transmitters from presynaptic nerve terminals and catecholamines from adrenal chromaffin cells. It is hypothesized that Pb2+ triggers secretion by directly interacting with the putative Ca-trigger receptor of the secretory exocytosis. In this project, isolated bovine chromaffin cells will be used a model system in further studies of the mechanism and molecular target(s) of lead's action(s) as secretagogue. (1) Entry and metabolism of Pb2+ in intact cells will be studied using a combination of fluorescence and atomic absorption spectroscopy, in order to elucidate in detail the relationship between intracellular Pb2+ accumulation and its effect on the basal and stimulus evoked secretory responses of chromaffin cells; (2) Permeabilized chromaffin cells will be employed to characterize the pharmacology and ionic selectivity of the process of Pb2+ induced secretion; (3) Attempts will be made to identify the molecular target(s) of Pb2+ action in secretion. The extraordinary sensitivity of the secretory process to pM concentrations of Pb2+ suggest that transmitter release and hormone secretion could be affected in low level lead exposure. Elucidation of the interactions between Pb2+ and secretory cell functions should advance our understanding on the cellular and molecular level of deleterious health effects of low level lead exposure. In addition, this research may provide useful insights into the fundamental mechanisms underlying the secretory process.
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