Effects of water-soluble carbodiimide on "fast" sodium channel gating in the rat sensory neuron membrane

Currents through "fast" (tetrodotoxin-sensitive) channels before and after external application of solutions containing 100 mM 1-ethyl-3-dimethylaminopropyl)carbodiimide-HCl (WSC) were measured during volage clamping at the membrane of dialyzed neurons of rat spinal ganglia. Treating the membrane with WSC (pH 4.8–4.9) led to a 5 to 20-fold reduction in sodium conductance, a 1.5–2.5-fold deceleration in the dynamics of current increase, and less abrupt voltage-dependent sodium channel activation curves. The shifted effective charge of activation was normally halved. The WSC produced no effect on activation parameters at normal pH (7.6). It was deduced that the changes observed resulted from WSC reacting with carboxyl groups located on the outer surface of the membrane. These groups are thought to be involved in the system of charge movements of the sodium channel gating mechanism.