Isolation of a Human κ Opioid Receptor cDNA from Placenta

By using a mouse δ opioid receptor cDNA as a probe, a κ opioid receptor gene was isolated from a human genomic library. Reverse transcriptase/PCR was subsequently used to isolate the corresponding cDNA from human placenta mRNA. Characterization of the cloned receptor with a κ agonist in transfected COS-7 cells, revealed a Kd of 0.67nM, which is similar to rodent κ1 receptors. In competition binding experiments, non-κ agonists had kis > 1000nM. Furthermore, when expressed in COS-7 cells, the κ receptor is negatively linked to cAMP. A Northern blot showed the presence of two transcripts, 6 and 7 kB in size, in both placenta and brain mRNA, which hybridized to the κ cDNA.