Purification of the 5-hydroxytryptamine 5-HT3 receptor from NCB20 cells

A 5-hydroxytryptamine 5-HT3 receptor binding site has been purified from deoxycholate-solubilized NCB20 cell membranes. Purification (1,700-fold) was achieved in one step by affinity chromatography with L-685,603 immobilized on agarose. The 5-HT3 selective antagonist [3H]Q ICS 205-930 labeled a single population of receptors in the affinity-purified preparation with a Bmax of 3.1 +/- 0.9 nmol/mg protein and Kd of 0.40 +/- 0.05 nM (mean +/- S.E., n = 3). The rank order of potency for a series of competing compounds confirmed that [3H]Q ICS 205,930 was labeling a 5-HT3 receptor in the purified preparation, and the inhibition constants for all antagonists were unchanged after purification. The purified 5-HT3 binding site eluted from a Sepharose 6B gel filtration column in a similar manner to the crude solubilized preparation (Stokes radius of 4.9 nm, apparent molecular size 250,000). Polyacrylamide gel electrophoresis of the affinity-purified receptor showed two broad bands by silver staining, migrating with apparent molecular masses of 54,000 and 38,000. Gel filtration of the affinity purified material yielded a single peak labeled by [3H]Q ICS 205-930 with an apparent molecular size of 250,000, which was also composed of two bands of 54,000 and 38,000, consistent with these being the constituents of the 5-HT3 receptor.