Epidemiological, behavioral, physiological and biochemical evidence indicates that lead (Pb) alters the functioning of the nervous system at very low concentrations. However, the cellular mechanisms by which Pb exerts its effects, at the very low concentrations found in vivo are largely unknown. The applicants propose to investigate four specific hypotheses concerning cellular mechanisms of low level Pb actions on the nervous system. (1) Pb acts as a Ca2+ surrogate in activating calmodulin. Among the multiple effects expected are stimulation of Ca2+-calmodulin-dependent protein kinase (CaM kinases) and enzymes involved in cyclic AMP metabolism. (2) In some proteins, particularly the Ca2+-dependent protein phosphate calcineurin and some Ca2+-permeable ion channels, Pb blocks Ca2+ binding and inhibits normal modulation of protein function by Ca2+. (3) Through actions on CaM kinases, calcineurin, and other intracellular signalling pathways, Pb increases protein phosphorylation. (4) These interactions cause Pb exposure to alter the functioning of cellular proteins, which in turn causes morphological and physiological effects, including increased dendritic branching and increased currents through some ion channels. The applicants plan an integrated approach, beginning with the effects of Pb on specific molecules in vitro and ending with hypothesized effects on neuronal morphology in vivo. They have four specific aims: (1) they will investigate actions of Pb at physiologically relevant concentrations on calmodulin activity, CaM kinases activity, calcineurin activity and cyclic AMP concentrations. They predict that Pb will stimulate calmodulin and CaM kinase activity, inhibit calcineurin activity and increase cyclic AMP concentrations. (2) They will investigate the effects of Pb at physiologically relevant concentrations, on voltage-sensitive calcium channels and the AMPA and NMDA subclasses of inotropic glutamate receptor/channels. They predict that Pb will enhance current flow by increasing channel phosphorylation and by reducing Ca2+-dependent inactivation. (3) They will investigate the effects of Pb on protein phosphorylation at physiologically relevant concentrations in vitro and in intact animals exposed to low levels of Pb in vivo. They predict that Pb will increase the phosphorylation of important cytoskeletal proteins and ion channel proteins. (4) They will investigate the effects of Pb exposure in vivo on the morphology of pyramidal neurons in the hippocampus. By increasing protein phosphorylation, the applicant hypothesizes that prenatal and early postnatal Pb exposure will increase dendrite branching of hippocampal neurons in vivo.
| Cabell, L; Audesirk, G (1993) Effects of selective inhibition of protein kinase C, cyclic AMP-dependent protein kinase, and Ca(2+)-calmodulin-dependent protein kinase on neurite development in cultured rat hippocampal neurons. Int J Dev Neurosci 11:357-68 |
