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Biomedical subjects

M S Lewis

Publications and source records attributed to M S Lewis.

At least 91 records · Page 5Linked to original sources
PubMed1981

Autoradiographic localization of muscarinic cholinergic receptors in rat brainstem.

We have localized muscarinic cholinergic receptors in the rat brainstem by a light microscopic autoradiographic method. Initially, we examined the kinetics and specificity of the binding of radiolabeled quinuclidinyl benzilate ([3H]QNB) in slide-mounted, frozen tissue sections to determine that we were labeling the muscarinic cholinergic receptors as they had been described previously in biochemical pharmacological studies. Subsequently, using optimal binding parameters to obtain high specific to nonspecific ratios, we labeled tissue sections and generated autoradiograms by the apposition of emulsion-coated coverslips. We found high concentrations of autoradiographic grains associated with many nuclei in the brainstem including the superior colliculus, nuclei of the lateral lemniscus, pontine nucleus, parabrachial nucleus, trigeminal nerve nucleus (V), the tegmental nuclei, nucleus of the facial nerve (VII), the locus coeruleus, the medial vestibular nucleus, cochlear nucleus, of the tractus solitarius, and nucleus of the hypoglossal nerve (XII). We conclude that muscarinic cholinergic effects of acetylcholine and important in the normal function of both the sensory and motor systems. We speculate on the possible mechanisms of action of certain cholinergic agents, such as the mechanism of anticholinergic compounds when used to treat motion sickness or anticholinesterase poisoning.

Animals↗
PubMed1980

Self-association of chicken gizzard filamin and heavy merofilamin.

Filamin is a high molecular weight (subunit Mr 250 000) actin-binding protein isolated from smooth muscle. The protein forms a gel when mixed with solutions of F-actin. A proteolytic fragment of filamin, heavy merofilamin (subunit Mr 240 000), generated by the action of Ca2+-activated protease binds to actin but does not produce gelation. We have studied the self-association properties of filamin and heavy merofilamin by direct examination in the electron microscope and by equilibrium sedimentation distribution studies in the ultracentrifuge. Filamin self-associates reversibly to form dimers; the free energy of dimerization is approximately 7 kcal/mol. Further association to form tetramer and multimer appears to be irreversible. Warming of filamin solutions accelerates aggregation. Heavy merofilamin does not appear to self-associate but is entirely monomeric. These studies suggest that filamin produces gelation of F-actin by binding to actin and then self-associating to cross-link actin filaments into a gel.

Animals↗
PubMed1976

Simulation studies of self-associating systems; discrimination between specific and isodesmic associations.

The possibilities of discriminating between definite and indefinite (isodesmic) modes of self-association are explored by fitting the different models to stimulated data, using non-linear least-squares curve-fitting to determine the fitting parameters for real and impostor models. It was found that over an extensive range of values for the equilibrium constant of a non-ideal isodesmic generating model, only a non-ideal monomer-dimer-tetramer-octamer was a successful impostor model. Some criteria for rejecting inappropriate models are discussed.

Binding Sites↗
PubMed1975

Determination of plasma and tissue levels of tyramine by radioimmunoassay.

Antibodies were prepared against tyramine. The antigen was prepared as follows: p-Aminohippuric acid was coupled to mBSA using a carbodiimide reagent. The amino group was diazotized an attached to the aromatif ring of TYR. The immunogen in Freund's complete adjuvant was injected into rabbits. The specificity of the resulting antibody was determined by radioimmunoassay. Using random-labeled TYR-3H, TYR, its metabolites, phenethylamine analogs, catecholamines, and certain amino acids were evaluated by a competitive binding assay method. With this technique 4 ng of TYR inhibited the binding of TYR-3H by 50%. The radioimmunoassay of TYR was used to measure the plasma, urine, and tissue levels of TYR in rabbits. The plasma disappearance curve of TYR revealed a biphasic pattern with t1/2 of 2 min and 54 min. The highest concentration of TYR was found in adrenals and spleen. The factthat the major metabolites of TYR and a series of pharmacologically important sympathomimetics and catecholamines did not interfere, makes the radioimmunoassay of TYR a useful, simple, sensitive, and spedific method for the direct analysis of TYR in biological meterials.

Animals↗