Pairs of Receptors (IMAGE) University of Würzburg Caption Using special ligands, it was possible to prove that opioid receptors are also present as pairs of two in the cell membrane. Credit (Picture: Scigraphix) Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.