Dynorphin-selective inhibition of adenylyl cyclase in guinea pig cerebellum membranes.
Guinea pig cerebellum, which contains kappa opioid receptors uncontaminated by other opioid receptor types, was chosen to examine whether kappa receptors are coupled to adenylyl cyclase. Membranes were prepared from guinea pig cerebellum and pretreated at pH 4.5 to increase inhibitory activity, and adenylyl cyclase was assayed in the presence of dynorphin analogs as prototypical kappa agonists. Results showed that several dynorphin analogs inhibited adenylyl cyclase by 30-50%, whereas mu- and delta-preferring agonists had no effect. Dynorphin A and the kappa-selective compounds D-Pro10-dynorphin(1-11) and U-50,488H were the most potent agonists, with IC50 values of 0.03-0.05 microM, whereas other dynorphin gene products like dynorphin B and alpha-neo-endorphin were approximately 10-fold less potent. Like other Gi-coupled responses, dynorphin-inhibited adenylyl cyclase required GTP and sodium. Naloxone was a competitive antagonist for dynorphin-inhibited adenylyl cyclase, with 1 microM naloxone shifting the IC50 value of dynorphin A by 20-fold. The kappa-selective antagonist nor-binaltorphimine was even more potent, with 0.1 microM nor-binaltorphimine shifting the dynorphin IC50 value by 50-fold. These results suggest that dynorphin A and its analogs inhibit adenylyl cyclase by binding to a guanine nucleotide-binding protein-coupled opioid receptor whose pharmacological specificity matches those of kappa receptors.
Konkoy
C S
CS
Department of Pharmacology, University of Florida College of Medicine, Gainesville 32610.
Childers
S R
SR
D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D002531:Cerebellum / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology; D003342:Corpus Striatum / Q000201:enzymology; D004399:Dynorphins / Q000494:pharmacology*; D006150:Guanine Nucleotides / Q000502:physiology; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D009270:Naloxone / Q000494:pharmacology; D011957:Receptors, Opioid / Q000502:physiology*; D017473:Receptors, Opioid, kappa; D012964:Sodium / Q000494:pharmacology
D000067956:Adenylyl Cyclase Inhibitors; D006150:Guanine Nucleotides; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D005576:Colforsin; D009270:Naloxone; D004399:Dynorphins; D012964:Sodium