Chronic exposure to lead causes persistent alterations in the electric membrane properties of neurons in cell culture.

The effects of chronic lead (Pb) exposure on neuronal electric membrane properties (EMP) were determined using neural cell cultures of adult mouse dorsal root ganglia (DRG). Cultures were exposed to Pb concentrations ranging from 0 to 100 microM for 12 days (8 DIV to 20 DIV). EMP were determined in Pb-free medium either immediately after withdrawal (IWD), or 6 days after withdrawal (6WD) from Pb. For IWD, regression analysis indicated that a number of EMP varied significantly with increasing Pb concentration. The largest such change occurred for electrical excitability which decreased significantly with increasing Pb (P = 0.000), being reduced by approximately two-thirds for neurons exposed to 100 microM Pb; resting membrane potential increased with Pb (P = 0.000); membrane time constant decreased with Pb (P = 0.007); action potential afterhyperpolarization decreased with Pb (P = 0.023). There was also evidence that the time course of action potentials was accelerated with increasing Pb concentrations, the rate of fall of neurons with biphasic falling phases being particularly increased (P = 0.047). This general pattern of altered EMP was observed for the 6WD condition also, indicating that chronic exposure to Pb caused persistent abnormalities in neuronal membranes even after 6 days of cultivation in Pb-free medium. The patterns of alterations in EMP suggested that chronic Pb exposure caused a prolonged increase in potassium permeability. It was proposed that the latter was mediated through a Pb-induced increase in intracellular ionic calcium and the associated disruption of calcium homeostasis.