Laboratory project: "Muscarinic Acetylcholine Receptors of Cultured Cell Lines"
Summary of work for this project as indicated on the report: "Our work on muscarinic acetylcholine receptors focuses on
two fundamental questions: (1) How is binding of acetylcholine to receptors converted into an intracellular response? (2)
What factors regulate receptor concentrations in the membrane? A binding assay employing tritiated quinuclidinyl benzilate
permits us to investigate properties of receptor binding sites and to measure receptor levels in cultured neuroblastoma and
hybrid cells under systematically varied conditions."
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2 (154,782 Bytes)
1976-09 (September 1976)
Nirenberg, Marshall W.
Klein, William L.
National Heart and Lung Institute. Laboratory of Biochemical Genetics
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From Neuroblastoma to Homeobox Genes, 1976-1992
Neuroblastoma Research, 1967-1976
Annual Report of the Laboratory of Biochemical Genetics, October 1, 1975 - September 30, 1976 (September 1976)
31 of 31
Project Number: Z01 HL 00012-02 LBG
Period Covered: July 1, 1975 through June 30, 1976
Title of Project: Muscarinic Acetylcholine Receptors of Cultured Cell Lines
Names, Laboratory and Institute Affiliations, and Titles of Principal Investigators and All Other Professional Personnel Engaged
on the Project:
PI: Marshall Nirenberg, Chief, Lab. of Biochemical Genetics, LBG NHLI
OTHER: William Klein, Postdoctoral Fellow, LBG NHLI
Orest Hurko, Staff Fellow, LBG NHLI
Wolfang Burgermeister, Guest Worker, LC NIAMDD
Bernhard Witkop, Chief, Laboratory of Chemistry, LC NIAMDD
Cooperating Units (if any): Laboratory of Chemistry, NIAMDD
Lab/Branch: Laboratory of Biochemical Genetics
Section: Section on Molecular Biology
Institute and Location: NHLI, NIH, Bethesda, Maryland 20014
Total Man Years: 2.5
Summary of Work:
Our work on muscarinic acetylcholine receptors focuses on two fundamental questions:
(1) How is binding of acetylcholine to receptors converted in an intra-cellular response?
(2) What factors regulate receptor concentrations in the membrane?
A binding assay employing tritiated quinuclidinyl benzilate permits us to investigate properties of receptor binding sites
and to measure receptor levels in cultured neuroblastoma and hybrid cells under systematically varied conditions.
Objectives: The objectives of our work have been (1) to characterize the nature of ligand interactions with muscarinic receptors,
and (2) to assess various factors likely to affect receptor concentrations. Although most methodology involved has been straightforward,
our experiments required the custom labeling and purification of muscarinic ligands as commercially available materials were
unsuitable due to low specific activity.
Major Findings: The principal findings are:
(1) Excitatory and inhibitory muscarinic receptors for ligands which do not differ pharmacologically.
(2) The affinity of receptors for acetylcholine is affected by the ionic composition of the medium.
(3) Antagonists and agonists differ strikingly in the way that they interact with the receptor. Antagonist binding to receptor
follows the law of mass action whereas agonist binding does not. When analyzed on Hill plots, agonist interactions with receptor
exhibit negative cooperativity that may be related to receptor desensitization.
(4) The receptor concentration is greatly reduced by exposure of cultured cells to carbamylcholine or other receptor activators.
The [receptor-agonist] complex is degraded more rapidly than the free receptor.
(5) Muscarinic excitatory and inhibitory acetylcholine receptors have been solubilized and have been characterized partially.
Significance to Biomedical Research: This work with a model system suggests that, in the normal nervous system, receptor
levels, which ultimately influence the pattern of behavior of neural nets, are regulated by synaptic transmission. Some of
the events which result from the interaction of acetylcholine with muscarinic acetylcholine receptors have been defined.
Two regulatory processes were found which depend upon acetylcholine. One regulates receptor activity, the other regulates
Proposed Course: Further elucidation of QNB binding will be pursued.