Disruption of neurotransmitter and hormone release is a likely factor in neurobehavioral, neuroendocrine, and endocrine disturbances associated with low-level lead (Pb2+) toxicity. The overall goal of this research is to assess the role of pb2+ interactions with calcium-signal transduction mechanisms, with focus on the Ca2+-dependent secretion of neurotransmitters and hormones. Previous results from our laboratory indicate the Pb2+ disrupts secretion by high affinity interactions with Ca2+-effector(s) of exocytosis. As an extention of these studies, the aim of the current project is to test a hypothesis that specific Ca2+-modulated lipid-binding proteins, calpactin I, synaptotagmin (p65), protein kinase C, and cytoplasmic form of phospholipase A2 (cPLA2) are important components of the secretory machinery and key targets for Pb2+-trigger action in secretion. The proteins will be isolated and their interaction with pb2+ characterized, using biochemical, biophysical, and immunochemical techniques. Permeabilized bovine adrenal chromaffin cells and cell-free models of exocytosis will be developed to further characterize the role of Pb2+ in the exocytotic mechanism. In addition to the interaction with the exocytotic apparatus, lead ions modify activity of calcium channels in the adrenal chromaffin cells through as yet undefined intracellular mechanism. Whole-cell voltage-clamp and single channel recordings from chromaffin cells in culture will be employed to test a hypothesis that low concentrations of intracellular Pb2+ modulate the l-type Ca2+ currents by slowing-down calcium-dependent channel inactivation. This research is expected to advance our understanding of Pb2+ actions in secretion at the molecular level and at the same time provide important information regarding the nature of exocytotic process itself. In Pb2+ interactions with Ca2+ signal transduction at different levels of cellular organization and may identify the Ca/lipid-binding proteins as major molecular targets in lead toxicity.
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