[Effect of a water-soluble carbodiimide on the gating mechanism of "fast" sodium channels of the sensory neuron membrane of the rat].

Currents through "fast" (tetrodotoxin-sensitive) sodium channels in dorsal root ganglion of rat were measured before and after the 5-6 min. external application of solutions containing 100 mM 1-ethyl-3 (3-dimethylaminopropyl) carbodiimide-HCl (WSC). The WSC treatment (pH 4.8-5.0) resulted in a decrease of the sodium conductance, slowing down of the activation kinetics by the factor of 1.5-2.5 and a decrease of the steepness of the activation curve. Effective charge of activation determined from the limiting logarithmic slope of the activation curve at potentials where channels just begin to open was reduced by the factor of 2.0. At normal pH (7.6) the WSC induced no changes in activation parameters. The results suggest that observed effects are due to the WSC interaction with carboxyl groups, situated at the external membrane surface. These groups may be incorporated in the gating mechanism of the sodium channel.