title: Reversible and irreversible binding of beta-funaltrexamine to mu, delta and kappa opioid receptors in guinea pig brain membranes.
abstract: The effect of beta-funaltrexamine (beta-FNA), an irreversible mu receptor blocker in isolated tissue bioassays, on mu, kappa and delta opioid receptor binding and the binding of beta-[3H]FNA were determined in guinea pig brain membranes. beta-FNA inhibited the binding of mu, kappa and delta opioid ligands to their receptors with Ki values of 2.2, 14 and 78 nM, respectively. Pretreatment of brain membranes with beta-FNA (less than 2 microM) followed by extensive washing inhibited mu binding and to a lesser degree delta binding, without changing kappa binding. The extent of the irreversible inhibition was dependent on the concentration of beta-FNA, and this inhibition on mu binding could be observed with as little as 1 nM beta-FNA. The irreversible inhibition of mu binding by beta-FNA pretreatment was due to a decrease in the number of binding sites with little change in Kd, and was more pronounced in the presence of increasing concentrations of NaCl. Specific binding of beta-[3H]FNA to opioid receptors was demonstrated. The rate of specific binding with 2 nM beta-[3H]FNA was rapid in the initial 10 min and did not reach maximum in 90 min. The dissociation of bound beta-[3H]FNA (5 nM added) by the addition of excess unlabeled naloxone reached maximum at 30 min with approximately 35% of specifically bound beta-[3H]FNA remaining. Mu opioids were most effective in preventing specific binding of beta-[3H]FNA when added before beta-[3H]FNA. Opioids added 1 hr after 2 nM beta-[3H]FNA could displace maximally only 70 to 75% of specific binding.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D003496:Cyclazocine / Q000031:analogs & derivatives / Q000378:metabolism; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000378:metabolism; D016308:Enkephalin, Leucine-2-Alanine; D004745:Enkephalins / Q000378:metabolism; D016314:Ethylketocyclazocine; D005033:Ethylmaleimide / Q000494:pharmacology; D006168:Guinea Pigs; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000378:metabolism; D009270:Naloxone / Q000378:metabolism; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000378:metabolism; D011957:Receptors, Opioid / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D004745:Enkephalins; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; D012965:Sodium Chloride; D016314:Ethylketocyclazocine; D004743:Enkephalin, Leucine; D009271:Naltrexone; D016308:Enkephalin, Leucine-2-Alanine; C024524:beta-funaltrexamine; D003496:Cyclazocine; D005033:Ethylmaleimide