The binding interactions of Ro 40-5967 at the L-type Ca²⁺ channel in cardiac tissue

Ro 40-5967 [(1S,2S)-2-[2[3-(2-benzamidopropyl]-methylamino]ethyl]-6-fluoro-1,2,3,4-tetrahydro-1-isopropyl-2-naphthyl-methoxyacetate] is a new Ca²⁺ channel antagonist active at L-type channels. Radioligand binding studies in cardiac tissue show that Ro 40-5967 does not inhibit 1,4-dihydropyridine binding, but does inhibit diltiazem, desmethoxyverapamil and SR 33557 binding with IC₅₀ values of 8 × 10^-9, 10^-8 and 5 × 10^-8 M, respectively. Equilibrium and kinetic binding studies showed that Ro 40-5967 inhibited both desmethoxyverapamil and SR 33557 binding in an apparently competitive manner. Ro 40-5967 defines an additional and possibly unique antagonist binding site on the L-type voltage-gated Ca²⁺ channel.