Effect of digitonin on the binding of opiate agonists and antagonists to membrane-bound and soluble opioid binding sites.
Treatment of rat or toad brain membranes with low concentrations of digitonin (0.01-0.1%) inhibits the binding of opioids to their receptors. Moreover, the binding of agonists is inhibited to a greater extent than that of antagonists. Inhibition of antagonist binding is completely and specifically reversed by sodium ions (200 mM) while agonist binding is not. The binding of opiates to toad brain membrane is significantly less sensitive to digitonin than the binding to rat brain membranes. The present results furnish an explanation for our previous findings, i.e. good yield of binding to (digitonin/NaCl) solubilized binding sites from rat brain can only be obtained with labeled opiate antagonists. Furthermore, they also explain why good yields of binding to the soluble opioid binding sites from toad brain can be obtained in the absence of sodium, while high concentrations of NaCl are required for mammalian brain, such as rat.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002024:Bufo marinus; D004072:Digitonin / Q000494:pharmacology*; D004174:Diprenorphine / Q000378:metabolism; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000378:metabolism; D016308:Enkephalin, Leucine-2-Alanine; D005048:Etorphine / Q000378:metabolism; D008297:Male; D009270:Naloxone / Q000378:metabolism; D010111:Oxymorphone / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*; D013045:Species Specificity
D011957:Receptors, Opioid; D004174:Diprenorphine; D009270:Naloxone; D005048:Etorphine; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine; D010111:Oxymorphone; D004072:Digitonin