Pharmacological characterization of zinc and copper interaction with the human alpha₁A-adrenoceptor

Metal ions have a major role in human health, and interact with many classes of receptors including the G-protein coupled receptors. In the peripheral system, zinc mainly accumulates in the soft prostate organ and, with copper, influences prostate disease progression, from normal to hypertrophic or cancerous states. The development of these pathologies may be influenced by the α₁A-adrenoceptor, the principal regulator of prostate tonicity. There is currently no information on possible interactions between metals and the α₁A-adrenoceptor. We therefore studied the effects of several mono- and divalent ions on this receptor subtype using binding and functional experiments performed on expressed cloned human α₁A-adrenoceptor. Regardless of the counter anion used, Zn²⁺ and Cu²⁺ interact with α₁A-adrenoceptor with apparent affinities in the low micromolar range. In addition, using specific binding experiments, we established that these ions acted as negative allosteric ligands on prazosin/α₁A-adrenoceptor interaction, but in a different manner from the allosteric modulator 5-(N-ethyl-N-isopropyl)-amiloride, suggesting distinct mode of interaction. In addition, the presence of Cu²⁺ weakly decreased epinephrine affinity, whereas the addition of Zn²⁺ shifted to the left the epinephrine binding curve, revealing a positive allosteric effect but only on half of the binding site. Finally, cell-based functional experiments demonstrated that Zn²⁺ and Cu²⁺ antagonized epinephrine activation in an insurmountable manner, by reducing agonist efficacy without any shift in the epinephrine activation curves. This study shows the interactions between metal ions and the α₁A-adrenoceptor with affinities compatible with physiological concentrations and suggests that zinc and copper may have a biological role in prostate function.