Modification of the Binding Sites for Local Anesthetics in Sodium Channels of Neuroblastoma Cells by Batrachotoxin and Aconitine

Effects of the tertiary amines, procaine and lidocaine, its quaternary derivative QX—314, and neutral benzocaine, on Na currents in internally perfused neuro-blastoma cells were studied using the suction-pipette voltage clamp technique (Kostyuk et al. 1975 ; Zubov et al. 1980). Neuroblastoma cells used were N18 A-l and NTR-1 subclones derived from C1300 line (Konobasova et al. 1981) and Neuro 2a clone (American Type Culture Collection, 1981). Changes in sodium currents (7 N a) caused by local anesthetics were examined both before and after modification of Na channels by batrachotoxin and aconitine. External administration of these toxins to the cell membrane was accompanied by repetitive (10 Hz) membrane stimulation to accelerate channel modification. The latter remained practically irreversible after the removal of batrachotoxin or aconitine from the solution. To avoid the effects of local anesthetics on the resting inactivation of Na channels, the holding potential, E h , was set at —130 140 mV level. The effects of local anesthetics on normal Na channels in neuroblastoma cells are qualitively similar to those in the nerve fibre (Khodorov 1978). Procaine, lidocaine (external administration) and QX—314 (internal administration) produce two phenomenologically different types of sodium current inhibitions: a steady block without conditioning stimulation, and a cumulative (use-dependent) block which develops during repetitive membrane pulsing. Benzocaine brings about a steady block only. Modification of Na channels by batrachotoxin in neuroblastoma cells as well as in nerve fibres (Khodorov 1978; Zaborovskaya 1979) eliminates the cumulative inhibition of 7 Na by amine local anesthetics. The cumulative effect was significantly reduced and in several experiments eliminated by aconitine, although aconitine modified Na channels undergo full incativation during membrane depolarization (Grishchenko et al. 1981).