Complex allosteric interaction of heparin with neurokinin-1 receptors.

The effects of several heparin preparations on rat striatal neurokinin-1 receptor labelling were investigated. A low concentration of heparin dose-dependently stimulated [125I]Bolton-Hunter substance P ([125I]BH-SP) binding to rat striatal membranes. This effect was mainly due to an increase of the association velocity reflected by a decrease of the equilibrium dissociation rate constant. A higher heparin concentration inhibited specific [125I]BH-SP labelling by a negative allosteric mechanism as a result of an increase of the dissociation velocity.