Relationship between kappa 1 opioid receptor binding and inhibition of adenylyl cyclase in guinea pig brain membranes.
Previously, we showed that kappa-selective ligands inhibit adenylyl cyclase in guinea pig cerebellar membranes. The present studies explore the relationship between kappa 1 binding sites (as determined with [3H]U-69,593 binding) and kappa 1-inhibition of adenylyl cyclase (using U-50,488H) in guinea pig brain membranes. Various kappa opioids displaced [3H]U-69,593 binding at a single site with subnanomolar affinities. These agonists were several hundred-fold weaker in inhibiting adenylyl cyclase, but for most agonists the rank order of adenylyl cyclase inhibition paralleled the displacement of kappa 1 binding. The correlation of IC50 values for both adenylyl cyclase and binding was significant except for alpha-neo endorphin, which was relatively weak at inhibiting adenylyl cyclase despite a Ki value of 0.08 nM versus kappa 1 binding. Comparison between kappa 1 binding and kappa 1-inhibited adenylyl cyclase across eleven guinea pig brain regions revealed that kappa 1-inhibited adenylyl cyclase was highest in the cerebellum, absent in thalamus and superior colliculus, and moderate in other regions. In most regions, kappa 1 binding correlated with the efficacy of kappa 1-inhibited adenylyl cyclase. However, the hippocampus had high levels of kappa 1-inhibited adenylyl cyclase despite low levels of kappa 1 binding, while cortex exhibited a high density of kappa 1 sites but a relatively low level of kappa 1-inhibited adenylyl cyclase. Reaction of cerebellar kappa receptors with beta-chlornaltrexamine (beta-CNA) blocked both kappa 1 binding and kappa 1-inhibited adenylyl cyclase. The effect of beta-CNA on kappa 1-inhibited adenylyl cyclase was to inhibit efficacy with little decrease in agonist potency, thus suggesting no significant level of kappa receptor reserve for this effector system.
Konkoy
C S
CS
Department of Physiology and Pharmacology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27157.
Childers
S R
SR
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D044482:Benzeneacetamides; D001665:Binding Sites; D002531:Cerebellum / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006624:Hippocampus / Q000378:metabolism; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D011759:Pyrrolidines / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D017473:Receptors, Opioid, kappa / Q000378:metabolism*
D000067956:Adenylyl Cyclase Inhibitors; D044482:Benzeneacetamides; D011759:Pyrrolidines; D017473:Receptors, Opioid, kappa; D009271:Naltrexone; C017120:chlornaltrexamine; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; C045444:U 69593