Lead ions close steady-state sodium channels in Helix neurons

Abstract

Extracellularly applied Pb 2+ (1–150 μM) induced an outward current ( I Pb) in intracellularly perfused snail neurons. The current-voltage relationship of the Pb 2+-induced current was linear over the potential range of −100 to −40 mV with negative slope conductance. The Pb-induced current was strongly dependent on the Na + gradient. The I Pb in intra- or extracellular K +- and Cl −-free or -rich solutions was almost the same as in control external and internal salines. The negative slope of the I– V curve and the decreased conductivity during Pb 2+ application suggested that I Pb is owing to the blocking of the resting Na conductance. Data obtained from single-channel measurements also supported this conclusion. Patch-clamp data showed that the steady-state Na channel has a conductance of 14pS and both closed and open time-distributions displayed single exponential character.