Strychnine-binding proteins in intestinal cells: novel brucine binding site with binding affinities for alkaloids.

The purpose of this work was to define the pharmacology of an intestinal epithelial [3H]strychnine binding site. Strychnine, brucine, verapamil and desmethoxyverapamil bind to small intestinal mucosal homogenates with nanomolar affinity at a site not related to the strychnine receptor, which is in the spinal cord. The antidiarrheal agents, fluperamide and loperamide, and several alkaloids have an order of magnitude lower affinity. Agents that bind to cytochrome P450IID6 also displace [3H]strychnine binding, which implies that the binding site may have some properties similar to the catalytic site of this cytochrome P450 enzyme.