NANOMOLAR CONCENTRATIONS OF LEAD SELECTIVELY BLOCK NEURONAL NICOTINIC ACETYLCHOLINE RESPONSES IN MOUSE NEUROBLASTOMA-CELLS

The effects of inorganic lead (Pb2+) on the ion currents mediated by (1) neuronal nicotinic acetylcholine (ACh) receptors, (2) serotonin 5-HT3 receptors, as well as (3) voltage-dependent Ca2+ and Na+ channels have been investigated in voltage clamped mouse neuroblastoma cells. The nicotinic ACh receptor-ion channel complex appeared more sensitive to Pb2+ than the other ion channels investigated. Low concentrations of Pb2+ (1 nm - 3 μm) reduced the peak amplitude of the ACh-induced inward current to 74%-10% of the control value in a concentration-dependent manner. However, between 10 μm and 100 μm Pb2+ the blocking effect was reversed, while the decay of the ACh-induced inward current was delayed. These effects of Pb2+ on the nicotinic receptor-mediated inward current can be described by the sum of two sigmoidal concentration-effect curves with an IC50 value of 19 nm and an EC50 of 21 μm and with slope factors of -0.5 and 0.8, respectively. The current mediated by 5-HT3 receptors was less potently blocked by Pb2+ (IC50 = 49 μm; slope factor = -0.3). In addition, Pb2+ blocked the ion current through voltage-dependent Ca2+ channels. The IC50 value of the concentration-effect curve of block of transient type Ca2+ channels by Pb2+ is 4.8 μm and the slope factor is -0.9. Voltage-dependent Na+ channels were not affected by Pb2+ up to 100 μm. At concentrations > 1 μm, Pb2+ also induced a noninactivating inward current. The present results show that modification of neuronal nicotinic receptor function may contribute to neurotoxic effects of Pb2+ poisoning. © 1990.