Voltage clamp analysis of sodium channels in normal and scorpion toxin-resistant neuroblastoma cells.
Sodium currents mediated by voltage-sensitive sodium channels in normal and scorpion toxin-resistant neuroblastoma cells were measured using a giga-ohm seal recording method in the whole cell patch configuration. The voltage and time dependence of sodium currents were similar in normal and mutant cell lines. Half-maximal activation occurred for test depolarizations in the range of -7 to -11 mV. Half-maximal inactivation occurred for pre-pulses in the range of -62 to -69 mV. Scorpion toxin from Leiurus quinquestriatus (100 to 200 nM) increased the time constant for sodium channel inactivation 6- to 9-fold, increased the peak sodium current 2.0 +/- 0.5-fold, shifted the voltage dependence of sodium channel activation 7 to 11 mV to more negative potentials, and made the voltage dependence of inactivation less steep. These effects were observed for both normal and scorpion toxin-resistant neuroblastoma cells. However, the effect of Leiurus toxin on the rate of inactivation was half-maximal at 1.7 nM for the parental cell line N18, in contrast to 5.4 or 39 nM for the scorpion toxin-resistant clone LV30 and 24 or 51 nM for LV10. These results show that scorpion toxin resistance results from a specific change in channel properties that does not impair normal function but causes an increase in the apparent KD for Leiurus toxin action on sodium channels.
D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004594:Electrophysiology; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials; D009154:Mutation; D009447:Neuroblastoma / Q000503:physiopathology*; D012604:Scorpion Venoms / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*
D007473:Ion Channels; D012604:Scorpion Venoms; D012964:Sodium