Single sodium channels from human ventricular muscle in planar lipid bilayers

Sodium channels from human ventricular muscle membrane vesicles were incorporated into planar lipid bilayers and the steady-state behavior of single sodium channels were examined in the presence of batrachotoxin. In symmetrical 500 mM NaCl the averaged single channel conductance was 24.7 +/- 1.3 pS and the channel fractional open time was 0.85 +/- 0.04. The activation midpoint potential was -99.5 +/- 3.1 mV. Extracellular tetrodotoxin blocked the channel with a k(1/2) of 414 nM at 0 mV. In 7 out of 13 experiments subconductance states were observed (9.2 +/- 1.2 pS). When sodium chloride concentration was lowered to 100 mM, single channel conductance decreased to 19.0 +/- 0.9 pS, steady-state activation shifted by -17.3 +/- 5.1 mV, tetrodotoxin sensitivity increased to 324 nM, and sub-conductance states were invariably observed in single channel records (7.9 +/- 0.7 pS). In the planar lipid bilayer system the properties of cardiac sodium channels from different species are not very different, but there are significant differences between sodium channels from human heart and from human CNS.