Different spatial distributions of sodium channels in the slowly and rapidly adapting stretch receptor neuron of the crayfish

Inward Na⁺ currents were studied, using a two-microelectrode intracellular voltage-clamp technique, in the slowly adapting (SA) and rapidly adapting (RA) stretch receptor neurons of the crayfish after the axons were cut at different distances from the soma. In the SA neuron, inward Na⁺ currents were recorded in the soma even when the axon was cut as close as 100 μm from the center of the soma, indicating the presence of Na⁺ channels in these parts. Also, two populations of Na⁺ channels seem to exist in the SA neuron. In the RA neuron, only minute Na⁺ currents were observed if the axon was shorter than 250 μm. The results strongly indicate that the voltage-gated Na⁺ channels in the SA and RA neurons have different distributions and that the difference in the spatial distribution of Na⁺ channel types may be important for the difference in firing properties in the two types of neurons.