EFFECTS OF STRYCHNINE ON IONIC CONDUCTANCES OF SQUID AXON MEMBRANE

¹ Biological Laboratories, Harvard University, Cambridge, Massachusetts and Department of Physiology and Pharmacology, Duke University Medical Center, Durham, North Carolina

The alkaloid strychnine, when applied at concentrations between 1 x 10^-4 and 1 x 10^-3 M, increased the duration and decreased the amplitude of action potentials in squid giant axons. Voltage clamp analyses showed that strychnine significantly altered several membrane parameters. Early currents were inhibited and the rate of inactivation was decreased several-fold. Late currents were more inhibited and the conductance curve was shifted in the direction of depolarization on the voltage axis. For large depolarizing steps, the late current displayed a distinct hump. The decrease from that hump is due to a strychnine-induced potassium inactivation. The magnitude and time constant of this inactivation are highly voltage dependent. The effects of strychnine are compared with those of several other neuroactive agents.