Enhancement of [3H]DAGO1 binding to rat brain by low concentrations of monovalent cations.
The effects of mono- and di-valent cations and the nonhydrolyzable guanyl nucleotide derivative 5'-guanylimidodiphosphate (Gpp(NH)p) on the binding of the selective, high affinity mu-opiate receptor agonist, [3H]DAGO ([3H]Tyr-D-Ala-Gly-Mephe-Gly-ol), to rat brain membranes were studied in a low ionic strength 5 mM Tris-HCl buffer. Na+ and Li+ (50 mM) maximally increased [3H]DAGO binding (EC50 values for Na+, 2.9 mM and Li+, 6.2 mM) by revealing a population of low affinity binding sites. The density of high affinity [3H]DAGO binding sites was unaffected by Na+ and Li+, but was maximally increased by 50 mM K+ and Rb+ (EC50 values for K+, 8.5 mM and Rb+, 12.9 mM). Divalent cations (Ca2+, Mg2+; 50 mM) inhibited [3H]DAGO binding. Gpp(NH)p decreased the affinity of [3H]DAGO binding, an effect that was enhanced by Na+ but not by K+. The binding of the mu-agonist [3H]dihydromorphine was unaffected by 50 mM Na+ in 5 mM Tris-HCl. In 50 mM Tris-HCl, Na+ (50 mM) inhibited [3H]DAGO binding by decreasing the density of high affinity binding sites and promoting low affinity binding. The effects of Na+ in 5 mM and 50 mM Tris-HCl were also investigated on the binding of other opiate receptor agonists and antagonists. [3H]D-Ala-D-Leu-enkephalin binding was increased and inhibited. [3H]etorphine binding increased and was unchanged, and both [3H]bremazocine and [3H]naloxone binding increased by 50 mM Na+ in 5 mM and 50 mM Tris-HCl, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Bolger
G T
GT
Laboratory of Bioorganic Chemistry, NIADDK, National Institutes of Health, Bethesda, MD 20892.
Marcus
K A
KA
Thibou
R
R
Skolnick
P
P
Weissman
B A
BA
D000818:Animals; D001496:Batrachotoxins / Q000494:pharmacology; D001575:Benzomorphans / Q000494:pharmacology; D001923:Brain Chemistry / Q000187:drug effects*; D002414:Cations, Monovalent / Q000494:pharmacology*; 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* / Q000493:pharmacokinetics; D005048:Etorphine / Q000494:pharmacology; D006150:Guanine Nucleotides / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D011957:Receptors, Opioid / Q000378:metabolism; D013696:Temperature
D001496:Batrachotoxins; D001575:Benzomorphans; D002414:Cations, Monovalent; D004745:Enkephalins; D006150:Guanine Nucleotides; D011957:Receptors, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D006165:Guanylyl Imidodiphosphate; D009270:Naloxone; D005048:Etorphine; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine; C027248:bremazocine