Potent Ca 2+ channel antagonist; binds allosterically to the a 1 -subunit of L-type Ca 2+ channels (K d = 20 pM), at a site distinct from other types of blocker. Shows some selectivity for vascular smooth muscle, inducing vasorelaxation without producing inotropic or chronotropic effects. Inhibits PDGF-stimulated smooth muscle cell proliferation.