Human brain sodium channels in bilayers

Sodium channels from human cortex were fused into planar lipid bilayers in the presence of batrachotoxin, and their single channel properties examined. Single channel slope conductance averaged 26 ps; tetrodotoxin block of the channels was voltage dependent with a K1/2 at 0 mV of 51 nM. The channel was asymmetrically selective for sodium over potassium. The permeability ratio (PNa/PK) equalled 3.3 when potassium was present only on the intracellular side of the channel, but it was 5.7 with potassium on the extracellular side. The average channel activation gating midpoint was -91 mV. These results indicate that sodium channels from human brain can be successfully studied both electrophysiologically and pharmacologically with the planar bilayer system.