title: The use of ascorbate as a probe of opioid receptor structure: evidence for two independent mechanisms of receptor destruction by ascorbate.
abstract: Ascorbate (20mM) pretreatment of brain membrane suspensions at 37 degrees produced a rapid irreversible loss of specific opioid binding. There was no reduction in specific 3H-halo-peridol binding. Ascorbate induced loss of opioid binding under these experimental conditions was not blocked by low concentrations of EDTA or MN++. In contrast, the slowly developing loss of opioid binding during exposure to 1 mM ascorbate at 23 degrees was completely inhibited by 10(-5)M EDTA or Mn++. At 37 degrees, D-isoascorbate, and several other reducing agents (glutathione, dithiothreitol, cysteine) produced a loss of opioid binding similar to that seen with ascorbate. It is concluded that 1 mM ascorbate at 23 degrees, and 20 mM ascorbate at 37 degrees, destroy opioid binding sites by two independent mechanisms. Lipid peroxidation is implicated at low ascorbate concentrations; a reductive process appears to be responsible for the ascorbate induced loss of binding at higher concentrations.
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D005048:Etorphine / Q000378:metabolism; D006168:Guinea Pigs; D006220:Haloperidol / Q000378:metabolism; D008054:Lipid Peroxides / Q000378:metabolism; D008297:Male; D008345:Manganese / Q000494:pharmacology; D010100:Oxygen; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects*; D013379:Substrate Specificity
chemical_list: D008054:Lipid Peroxides; D011957:Receptors, Opioid; D005048:Etorphine; D008345:Manganese; D004492:Edetic Acid; D006220:Haloperidol; D001205:Ascorbic Acid; D010100:Oxygen