Curve manipulations were performed using pClamp8 (Axon In-
struments) and Origin software (Microcal, USA). Voltage-dependence
of activation was determined from the I–V curves and the reversal
potential was measured experimentally for each oocyte. The voltage
dependence of relative current (activation and fast inactivation) was fit
by a Boltzmann function.
BTX was kindly provided by John Daly (N.I.H., USA). The mo-
lecular weight was checked on a LCQ Deca XP iontrap mass spec-
trometer (Finnigan Corp., USA)