Organized Cultures of Nerve Tissue: A Novel Model System for Studies of Lipid Protein Interaction on the Functional Level
The glycine carrier is a transversal protein that is governed by phosphatidylcholine (PC) but not by phosphatidylethanolamine (PE) in a fatty acid specific fashion. PC binds the ligand as well as it affects the protein. The carrier does not undergo lateral motion between ordered and fluid lipid domains. On the whole the glycine carrier is a protein with relatively little functional relation to the compositional mosaicism of the plasma membrane.
The GABA carrier is a mobile protein that seems to be localized to a major extent in the outer leaflet. Asymmetrically distributed PL regulate the activity of the protein in a fatty acid specific manner. The carrier can be inhibited as well as stimulated.
The GABA receptor is not a lipoprotein in nature. PL affect the receptor activity either through a single transversal modulator protein or through two asymmetrically distributed modulator proteins. PL that are components of the outer leaflet such as phosphatidyl-N-dimethylethanolamine (PDE) activate the inhibitory capacity of the modulator leading to a state of desensitization of the receptor that is characterized by an increase in the strength of ligand binding. Cytoplasmic PL, among them mainly PE and phosphatidyl-N-monoethanolamine (PME), induce a stimulation of GABA receptor binding through activation of the inner part of the transversal modulator or of the cytoplasmic modulator, thus creating a state of super-sensitivity. Cholinergic excess stimulation of the network of cultured neurons by bath application of carbachol increases PDE formation via the methylation pathway. This is accompanied by desensitization of the GABA receptor. The state of desensitization should be terminated through PE. The findings illustrate the functional specificity of PL in nerve tissue. It seems to be essential that viable cells are used since results stemming from artificial membranes of membrane preparations are not always the same.
KeywordsGaba Receptor Polar Head Outer Leaflet Viable Nerve Cell Gaba Transport
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