The sodium channel from rat brain. Reconstitution of voltage-dependent scorpion toxin binding in vesicles of defined lipid composition.
Purified sodium channels incorporated into phosphatidylcholine (PC) vesicles mediate neurotoxin-activated 22Na+ influx but do not bind the alpha-scorpion toxin from Leiurus quinquestriatus (LqTx) with high affinity. Addition of phosphatidylethanolamine (PE) or phosphatidylserine to the reconstitution mixture restores high affinity LqTx binding with KD = 1.9 nM for PC/PE vesicles at -90 mV and 36 degrees C in sucrose-substituted medium. Other lipids tested were markedly less effective. The binding of LqTx in vesicles of PC/PE (65:35) is sensitive to both the membrane potential formed by sodium gradients across the reconstituted vesicle membrane and the cation concentration in the extravesicular medium. Binding of LqTx is reduced 3- to 4-fold upon depolarization to 0 mV from -50 to -60 mV in experiments in which [Na+]out/[Na+]in is varied by changing [Na+]in or [Na+]out at constant extravesicular ionic strength. It is concluded that the purified sodium channel contains the receptor site for LqTx in functional form and that restoration of high affinity, voltage-dependent binding of LqTx by the purified sodium channel requires an appropriate ratio of PC to PE and/or phosphatidylserine in the vesicle membrane.
D J
DJ
Feller
J A
JA
Talvenheimo
W A
WA
Catterall
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002412:Cations; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007473:Ion Channels / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D010743:Phospholipids / Q000502:physiology*; D051381:Rats; D012604:Scorpion Venoms / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D002412:Cations; D007457:Iodine Radioisotopes; D007473:Ion Channels; D010743:Phospholipids; D012604:Scorpion Venoms; D012964:Sodium