title: Muscarinic receptors in porcine caudate nucleus. I. Enhancement by nickel and other cations of [3H]cis-methyldioxolane binding to guanyl nucleotide-sensitive sites.
abstract: Muscarinic acetylcholine receptors in the synaptic membrane fraction of porcine caudate nucleus were characterized by using a radiolabeled agonist, [3H]cis-methyldioxolane [( 3H]CD) and an antagonist, [3H]quinuclidinyl benzilate [( 3H]QNB). Scatchard analysis of the specific binding of [3H]CD gave a single equilibrium dissociation constant of 8.1 nM when a concentration of less than 80 nM [3H]CD was used. The binding capacity was 390 fmoles/mg of protein and corresponded to about 10% of the binding sites of [3H]QNB. Agonist/[3H]CD competition binding experiments indicated that [3H]CD was selectively bound to the sites with a high affinity for agonists. [3H]CD binding was inhibited by Na+, K+, Mg2+, and Ca2+ with the half-maximal effect at 10-50 mM. Nickel ion showed biphasic effects on [3H]CD binding: a 2- to 3-fold enhancement of binding at 0.1-10 mM and inhibition above 10 mM. Other cations, including Co2+, Mn2+, and Zn2+, at 1 mM also increased [3H]CD binding by a factor of 1.5-1.8. Among 18 cations examined, only Cd2+, Hg2+, and Cu2+ caused significant inhibition of [3H]CD binding at 1 mM. [3H]CD binding was decreased to about 20% of the control value in the presence of guanylyl-5'-imidodiphosphate (GppNHp), GTP, and GDP with the half-maximal effect at 1.3, 32, and 45 microM, respectively. [3H]CD binding in the presence of Ni2+ was decreased by GppNHp to a level obtained in the presence of GppNHp alone. The increase caused by Ni2+ in [3H]CD binding was due to the increase in the maximal binding capacity (Bmax) without changes in the affinity for [3H]CD. We conclude that Ni2+ increases the proportion of a muscarinic receptor subclass (or state) that is sensitive to guanyl nucleotide.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002412:Cations / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology; D002421:Caudate Nucleus / Q000378:metabolism*; D004148:Dioxolanes / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D009532:Nickel / Q000494:pharmacology*; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D013552:Swine; D013570:Synaptic Membranes / Q000378:metabolism
chemical_list: D002412:Cations; D002413:Cations, Divalent; D004148:Dioxolanes; D006150:Guanine Nucleotides; D011976:Receptors, Muscarinic; D006165:Guanylyl Imidodiphosphate; C024310:2-methyldioxolane; D011813:Quinuclidinyl Benzilate; D009532:Nickel