GABA interaction with lipids in organic medium.
The interaction of 3H-GABA (gamma-aminobutyric acid and 14C-glutamate with lipids in an aqueous organic partition system was studied. With this partition system 3H-GABA and 14C-glutamate were able to interact with sphingomyelin, sulfatide, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine and phosphatidic acid but not with cholesterol or ceramide. In an homogeneous aqueous medium we could not demonstrate any interaction between 3H-GABA and lipids. The apparent dissociation constants (Kd) for 3H-GABA-lipids or 14C-glutamate-lipids interactions in organic medium were in the millimolar range and maximal charge (Bmax) between 3 and 7 moles of GABA or glutamate by mole of lipid. Amino acids such as glutamic acid, beta-alanine and glycine displaced 3H-GABA with the same potency as GABA itself; thus these results show that the interaction lacks pharmacological specificity. To detect this interaction lipid concentrations higher than 2 microM were required and in the partition system 3H-GABA and lipid phosphorus were both concentrated at the interface. Therefore lipids tested with a biphasic partition system do not fulfill the classical criteria for a neurotransmitter receptor at least not for GABA and glutamate.
D000596:Amino Acids / Q000378:metabolism; D001667:Binding, Competitive; D002725:Chloroform / Q000494:pharmacology; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D050356:Lipid Metabolism; D000432:Methanol / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism; D012997:Solvents; D013109:Sphingomyelins / Q000378:metabolism; D013433:Sulfoglycosphingolipids / Q000378:metabolism; D014316:Tritium; D014867:Water; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000596:Amino Acids; D005971:Glutamates; D010743:Phospholipids; D012997:Solvents; D013109:Sphingomyelins; D013433:Sulfoglycosphingolipids; D014867:Water; D014316:Tritium; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D002725:Chloroform; D000432:Methanol