Abstract
The purified saxitoxin (STX) binding component of the rat sarcolemmal sodium channel (SBC) has been reconstituted into phospholipid vesicles. The reconstituted SBC displays the pharmacological properties and the ability to control sodium fluxes expected of a functional sodium channel. Batrachotoxin (BTX) increases 22Na+ influx into reconstituted SBC vesicles by greater than 100% over control at early time points. The BTX-stimulated 22Na+ influx is specifically and quantitatively blocked by STX. Veratridine and aconitine also stimulate Na+-flux--although less effectively than BTX--in the order: BTX greater than veratridine greater than aconitine. The logarithmic dose--response curves for BTX and veratridine are sigmoidal with a K0.5 of 1.5 microM and 35 microM, respectively. Vesicles containing the reconstituted SBC demonstrate 3H-labeled STX binding to a single class of high affinity sites witha Kd of 5--7 nM at 0 degrees C; the thermal stability of the STX receptor is markedly enhanced by reconstitution. Our results confirm that the purified STX binding component from rat sarcolemma constitutes the sodium channel itself and contains at least those components sufficient for channel activation, transmembrane ion movement, and inhibition by STX.
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