Use of [3H]spiperone for labelling dopaminergic and serotonergic receptors in bovine caudate nucleus

[3H]Spiperone binding has been used to study neurotransmitter receptors in bovine caudate nucleus in displacement and saturation binding experiments. Displacement curves for several antagonists are biphasic and can be analysed into contributions from dopaminergic and serotonergic sites. Antagonist binding at each class of sites follows the simple mass action equations for binding at a homogeneous set of sites (slope factors close to unity). Agonist displacement curves also indicate complex behaviour, but agonist binding to the dopaminergic sites alone exhibits heterogeneous properties (slope factors less than unity). Saturation binding experiments have been conducted on each class of site, defining dopaminergic binding of [3H]spiperone as that binding displaced by 0.1 mM-dopamine and serotonergic binding as that displaced by 0.3 microM-mianserin. In each case, a single class of binding sites was detected: the binding parameters derived in this way have been used to calculate the proportions of the two classes of binding site observed in displacement experiments. Good agreement was obtained between calculated and observe values.

The binding of some antidepressant drugs to brain muscarinic acetylcholine receptors

1 The binding of some antidepressant drugs, including some new drugs of atypical structure (flupenthixol, iprindole, maprotiline, mianserin, nomifensine, tofenacine and viloxazine) to muscarinic acetylcholine receptors in the brain has been studied by displacement of [3H]-atropine. 2 Many of the drugs are potent muscarinic antagonists. 3 Some correlation can be made between the affinity for binding to the muscarinic acetylcholine receptor and the incidence of anticholinergic side effects in clinical usage.

A method for measuring relative changes in guanosine 3':5'-cyclic monophosphate in mouse neuroblastoma cells on muscarinic cholinergic stimulation

A convenient, inexpensive assay was developed for measuring relative changes in cyclic GMP in whole mouse neuroblastoma cells (clone NIE 115) based on labelling the cellular GTP pool with [8(-3)H]guanine. The time course of cell labelling and the distribution of radioactivity among possible products were studied; GTP is the only major labelled species. Radioactive cyclic GMP produced from the radioactive GTP on cell stimulation is isolated by column chromatography nad its identity has been rigorously established by paper chromatography and ion-exchange chromatography. The assay was used to study the time course of the cyclic GMP changes that occur after stimulation of neuroblastoma cells with carbamoylcholine and the dependence of the cyclic GMP changes on the carbamoylcholine concentration. The assay gives results comparable with those obtained by using a radioimmunoassay for cyclic GMP and should be applicable to other whole-cell and tissue-slice systems.

Ligand-binding propeties of the muscarinic acetylcholine receptor in mouse neuroblastoma cells

1. Muscarinic acetylcholine receptors in a plasma-membrane fraction derived from mouse neuroblastoma clone NIE-115 bind [3-3H]quinuclidinyl benzilate according to the Law of Mass Action (Kdissociation 40 pM, h0.96). 2. Antagonist and agonist binding to the receptor was studied by displacement of [3-3H]quinuclidinyl benzilate with non-radioactive ligands. The data show good agreement with similar data obtained on rat brain and ideal smooth muscle [Birdsall & Hulme (1976) J. Neurochem. 27, 7-16] indicating that the receptor is very similar in these three tissues.

Properties of the galactose binding protein of Salmonella typhimurium and Escherichia coli

The galactose binding protein implicated in transport and in chemotaxis has been purified to homogeneity from the shock fluids of Salmonella typhimurium and Escherichia coli. Both proteins are monomers of molecular weight 33 000 and exhibit cross-reactivity with antibody. The Salmonella galactose receptor showed binding of 1 mol of [14C]galactose or 1 mol of [14C]glucose at saturation. The dissociation constants were 0.38 and 0.17 muM, respectively. In light of the previously published report that the E. coli protein contains two binding sites with two different affinities, the binding characteristics of this protein were reexamined. Using highly purified radiolabeled substrate and homogeneous protein, a single binding site and single binding affinity were seen galactose (KD = 0.48 muM) or for glucose (KD = 0.21 muM). The competition between glucose and galactose for the same site is intriguing in view of the competition between ribose and galactose at the receptor level.

Receptor interactions in a signalling system: competition between ribose receptor and galactose receptor in the chemotaxis response

Galactose and ribose receptors are shown to compete for a common site by comparing the specificities of the purified receptors with the specificity of the whole organism response. Ribose does not bind to the purified galactose receptor but inhibits the in vivo galactose response. A mutant lacking the ribose receptor shows no inhibition of the galactose response even at very high ribose concentrations. The results can be explained by a mechanism involving (a) a ligand-induced conformational change in the receptor which produces a combining site with affinity for the molecule that serves as a first component of the signalling system and (b) a limited number of such first component molecules that cannot bind both receptors simultaneously. The mechanism may have considerable generality for sensory, hormonal, and transport systems.