Reduced high-affinity agonist binding at the M(1) muscarinic receptor in Alzheimer's disease brain: differential sensitivity to agonists and divalent cations.
M(1) muscarinic acetylcholine receptor (M(1)AchR)-G protein coupling, as measured by high-affinity agonist binding, was examined in membranes prepared from postmortem human temporal cortex (Brodmann area 38) from individuals with Alzheimer's disease (AD, n = 8) and age-matched controls (n = 6). Binding competitions between the M(1)AchR-selective antagonist [(3)H]pirenzepine ([(3)H]PZ) and muscarinic agonists carbachol, acetylcholine, oxotremorine, and oxotremorine M were conducted. In the presence of 1 mM MgCl(2), the inhibition of [(3)H]PZ binding by carbachol, acetylcholine, or oxotremorine M was best described by a two-affinity state model for control and AD cases, while oxotremorine binding affinity was best fit to a single-state model. Although both control and AD groups had similar K(D) values for the high- and low-affinity agonist binding sites, the proportion of M(1)AchRs exhibiting high affinity for carbachol and acetylcholine was reduced by 48 and 33%, respectively, in AD membranes relative to controls (P < 0.05). No changes in the binding of the oxotremorine M or oxotremorine were noted. The nonhydrolyzable guanine nucleotide GppNHp (100 microM) reduced the proportion of M(1)AchRs with high affinity for agonists in both control and AD membranes. Substitution of 1 mM MnCl(2) for MgCl(2) restored high-affinity carbachol binding at the M(1)AchR in AD membranes similar to that seen in controls. In the presence of 1 mM MnCl(2), agonist binding in controls did not differ from 1 mM MgCl(2). In the absence of cations (1 mM EDTA), no differences between control and AD M(1)AchR carbachol binding were observed. Thus, the loss of high-affinity agonist binding at the M(1)AchR in AD is dependent on the agonist and cation studied.
Ladner
C J
CJ
Section of Neuropathology, Loyola University Chicago, Maywood, Illinois, 60153, USA.
Lee
J M
JM
D000109:Acetylcholine / Q000494:pharmacology; D000368:Aged; D000544:Alzheimer Disease / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D002712:Chlorides / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D005260:Female; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology; D008297:Male; D017895:Manganese Compounds / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000493:pharmacokinetics / Q000494:pharmacology*; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000494:pharmacology; D010890:Pirenzepine / Q000378:metabolism; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism*; D012016:Reference Values
D002413:Cations, Divalent; D002712:Chlorides; D017895:Manganese Compounds; D018721:Muscarinic Agonists; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic; D015636:Magnesium Chloride; D006165:Guanylyl Imidodiphosphate; D010890:Pirenzepine; D010095:Oxotremorine; C042743:oxotremorine M; D002217:Carbachol; D004492:Edetic Acid; D000109:Acetylcholine; C025340:manganese chloride