Single-channel analysis of Pb2+ modified steady-state Na-conductance in snail neurons

Patch-clamp technique was used in order to study properties of the steady-state Na-channel in snail neurons. Experiments revealed that Pb-ions, applied extracellularly, close these channels, which are preferably in open state at the resting membrane potential. Elementary currents have a linear current-voltage (I-V) relationship with single channel conductance of 14 pS between -100 and -40 mV both in control saline and in the presence of 50 microM Pb in the pipette. Pb-ions decreased the mean open and increased the mean closed time. It was found that both open and closed times showed little voltage-dependence, however the probabilities of the open and closed times proved to be voltage-dependent. Open and closed time histograms were fitted by one exponential, therefore first order kinetics were assumed for the blocking effect of Pb2+ at the single channel level.