Isopilocarpine binding to muscarinic cholinergic receptors

Isopilocarpine coexists with pilocarpine in nature, and it is present in varying degrees in commercial pilocarpine preparations. Using muscarinic cholinergic receptors from bovine ciliary muscle tissue, we measured the relative binding affinity of isopilocarpine and pilocarpine. The binding affinity of isopilocarpine was approximately one-tenth that of pilocarpine. Because of the relatively low concentration of isopilocarpine found in commercial pilocarpine preparations, and the low binding affinity of isopilocarpine for the muscarinic receptors, the practical effect of isopilocarpine contamination is small.