TY - JOUR T1 - Identification and Characterization of Three New Alternatively Spliced μ-Opioid Receptor Isoforms JF - Molecular Pharmacology JO - Mol Pharmacol SP - 396 LP - 403 DO - 10.1124/mol.56.2.396 VL - 56 IS - 2 AU - Ying-Xian Pan AU - Jin Xu AU - Elizabeth Bolan AU - Catherine Abbadie AU - Albert Chang AU - Amy Zuckerman AU - Grace Rossi AU - Gavril W. Pasternak Y1 - 1999/08/01 UR - http://molpharm.aspetjournals.org/content/56/2/396.abstract N2 - We have identified four new μ-opiod receptor (MOR)-1 exons, indicating that the gene now contains at least nine exons spanning more than 200 kilobases. Replacement of exon 4 by combinations of the new exons yields three new receptors. When expressed in Chinese hamster ovary cells, all three variants displayed high affinity for μ-opioid ligands, but κ and δ drugs were inactive. However, there were subtle, but significant, differences in the binding profiles of the three variants among themselves and from MOR-1. Immunohistochemically, the major variant, MOR-1C, displayed a regional distribution quite distinct from that of MOR-1. Region-specific processing also was seen at the mRNA level. Antisense mapping revealed that the four new exons were all involved in morphine analgesia. Together with two other variants generated from alternative splicing of exon 4, there are now six distinct MOR-1 receptors. ER -