[2-component nature of the displacement currents in a nerve fiber membrane: a kinetic and pharmacological analysis].

Asymmetrical displacement currents in the Ranvier node membrane were recorded in the normal Ringer and under the action of a neurotoxin from the scorpion Buthus eupeus venom and of the alcaloid aconitine. In the total displacement current (DC) at the beginning of the pulse (Ion), two-exponentially decaying components were extracted: a rapid component with the maximum time constant of decay about 70 microns, and a slower one with the time constant of decay--300 microns. At high negative levels of conditioning prepulse (Vc) (-130 divided by -145 mV), the maximum value of the charge transferred by the fast and slow components was estimated to be 2.6 x 10(-14) and 4.8 x 10(-14) C, respectively. The slow component of Ion decreased with lowering Vc and was inhibited by the scorpion neurotoxin and aconitine. The fast phase of Ion remained unchanged with decreasing Vc from -145 to -100 mV and toxin-treated axons. Aconitine evoked a shift in the curve relating the change displaced by the fast component to the membrane potential in the direction of hyperpolarization by 40--50 mV. The results obtained suggest that the fast and the slow components of DC are associated with the initial potential-dependent stages of the processes of channel activation and inactivation, respectively.