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Biomedical subjects

M G McNamee

Publications and source records attributed to M G McNamee.

At least 73 records · Page 4Linked to original sources
PubMed1981

Alteration of acetylcholine receptor and acetylcholinesterase metabolism by actinomycin D in cultured muscle cells.

Actinomycin D (ACT-D), an inhibitor of transcription, was added to chick muscle cultures to study its effect on the synthesis of acetylcholine receptor (ACHR) and acetylcholinesterase (ACHE, EC 3.1.1.7). Doses of ACT-D (1.85-18.5 nM), which inhibited uridine incorporation up to 80%, increased ACHR, ACHE, and creatine kinase (CK, EC 2.7.3.2) levels without affecting general cell protein. Degradation of ACHR was slower in ACT-D treated cultures than controls, resulting in a twofold increase in receptor half-life. Uridine incorporation was inhibited by ACT-D in both mononucleated cells and myotubes and [3H]uridine nuclear grain distribution were shifted to values lower than controls. The results indicate that posttranscriptional effects of ACT-D increase levels of ACHR, ACHE, and CK and that decreased degradation could account for the increase in the number of surface ACH receptors.

Acetylcholinesterase↗
PubMed1981

Molecular forms of acetylcholinesterase in chick embryonic fast muscle: developmental changes and effects of DFP treatment.

Multiple molecular forms of acetylcholinesterase (AChE) from embryonic chick pectoral muscle were examined by sucrose density sedimentation. Embryonic muscle in ovo possessed three molecular forms with apparent sedimentation coefficient of 7S, 11S, and 20S. The proportion of the 20S form increased 4-fold between days 11 and 18 in ovo and there was a decrease in the proportion of the 7S and 11S forms. Cultured embryonic muscle contained only 7S and 11S AChE despite the presence of the 20S form in the tissue from which the cultures were derived. Brief treatment with diisopropylphosphorofluoridate (DFP) completely inhibited the enzyme activity; the newly synthesized AChE first appeared as a 7S form. Polyacrylamide gel electrophoresis of the peak fractions from the sucrose gradients revealed that the 7S AChE was composed of two electrophoretic forms and gave evidence that the 20S AChE was too large to enter the running gel. The results are consistent with the ideas that the distribution of AChE molecular forms is regulated during embryonic development and that AChE is first synthesized as a low molecular weight form following inhibition with organophosphate compounds.

Acetylcholinesterase↗
PubMed1980

Inhibition of ion permeability control properties of acetylcholine receptor from Torpedo californica by long-chain fatty acids.

The characteristics of fatty acid inhibition of acetylcholine receptor function were examined in membrane vesicles prepared from Torpedo californica electroplax. Inhibition of the carbamylcholine-induced increase in sodium ion permeability was correlated with the bulk melting point of exogenously incorporated fatty acids. Above its melting temperature, a fatty acid could inhibit the large increase in cation permeability normally elicited by agonist binding to receptor. Below its melting temperature, a fatty acid was ineffective. None of the fatty acids altered any of the ligand binding properties of the receptor. Inhibitory fatty acids did not induce changes in membrane fluidity, as determined by electron paramagnetic resonance using spin-labeled fatty acids. The spin-labeled fatty acids also acted as inhibitors, and the extent of inhibition depended largely on the position of the nitroxide group along the fatty acid chain. Addition of noninhibitory fatty acid to the vesicle membranes did not protect the receptor from inhibition by spin-labeled fatty acids. The effects of free fatty acids on acetylcholine receptor function are attributed to the disruptions of protein-lipid interactions.

Acetylcholine↗
PubMed1980

Independent activation of the acetylcholine receptor from Torpedo californica at two sites.

Membrane vesicles enriched in acetylcholine receptor were prepared from the electroplax tissue of Torpedo californica. The receptor was reduced with dithiothreitol to expose a sulfhydryl group near the ligand binidng site and then treated in one of the following ways: (1) affinity alkylated treated in one of the following ways: (1) affinity alkylated with bromoacetylcholine, a receptor activator, (2) affinity alkylated with maleimidobenzyltrimethylammonium, a receptor inhibitor, or (3) reoxidized to the native state with dithiobis(2-nitrobenzoate). The affinity labels blocked half of the binding sites for alpha-bungarotoxin. The toxin sites not protected by the affinity labels were protected by carbamylcholine based on studies of toxin binding kinetics. The functional response of native and affinity-alkylated receptors was measured by a sodium ion flux procedure. In the absence of added cholinergic activators, only slow ion flux was observed. In the presence of carbamylcholine, a receptor activator, both native and modified membranes showed the increased sodium flux associated with functional receptors. The concentration of carbamylcholine required for a 50% maximal response was higher in the affinity-labeled membranes. Preincubation of the membranes with carbamylcholine blocked the increased ion flux, indicating that desensitization could be induced. The results provide evidence for the existence of two functional sites on the acetylcholine receptor. Each site corresponds to a bungarotoxin binding site and can be independently activated and desensitized.

Acetylcholine↗
PubMed1974

Distribution and fate of synthetic lipid vesicles in the mouse: a combined radionuclide and spin label study.

Single compartmental spherules of various lipid constituents (vesicles), enclosing (99m)TcO(4) (-) as a radioactive marker, were injected intravenously into C(3)H mice, and the distribution of radioactivity was studied. About 25% of the administered radioactivity was present in the liver 5 min and 30 min after the injection of vesicles composed of phosphatidylcholine and gangliosides, which were sonicated for 5 min (standard preparation). About 10-20% of the radioactivity remained in the circulation. By use of a nonradioactive spin label (tempocholine) enclosed within vesicles, intact vesicles were demonstrated in the circulation for 46 min after intravenous injection. The distribution of radioactivity from (99m)TcO(4) (-) inside vesicles is very different from that of free (99m)TcO(4) (-) or of (99m)Tc sulfur colloid. Increase in the length of sonication or incorporation of cholesterol into the wall of the vesicles enhanced hepatic levels and reduced blood levels of radioactivity. These same manipulations also slowed the rate of transfer of (99m)TcO(4) (-) out of vesicles in dialysis experiments in vitro. Addition of phosphatidic acid, phosphatidylethanolamine, or phosphatidylserine to the standard constituents did not greatly alter the distribution of radioactivity in vivo but did increase the number and type of active coupling sites on the outside of the vesicle. The results indicate that vesicles might be valuable as carriers of diagnostic or therapeutic agents.

Animals↗