Pharmacological characterization of zinc and copper interaction with the human alpha(1A)-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 α(1A)-adrenoceptor, the principal regulator of prostate tonicity. There is currently no information on possible interactions between metals and the α(1A)-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 α(1A)-adrenoceptor. Regardless of the counter anion used, Zn(2+) and Cu(2+) interact with α(1A)-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/α(1A)-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 Cu(2+) weakly decreased epinephrine affinity, whereas the addition of Zn(2+) 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 Zn(2+) and Cu(2+) 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 α(1A)-adrenoceptor with affinities compatible with physiological concentrations and suggests that zinc and copper may have a biological role in prostate function.