Butanol extracts from myelin fragments: identification of 5-hydroxytryptamine binding components

To investigate the nature of 5-HT binding components originated from myelin butanol extracts (i.e. proteolipids), the recombinate experiments with acidic lipids were planned. Binding assay of 14C . 5-Ht to recombinates was carried out by Sephadex lh20 column chromatography. Among several recombinate fractions, recombinate of sulphatides, phosphatidylserine and phosphatidylinositol showed the same elution profile and binding capacity for 14C . 5-HT with those of the myelin extracts. The displacement studies with other neurotransmitters revealed that the recombinate of these three acidic lipids completely regenerated the specificity of the original myelin proteolipids. Namely, tryptamine, DA and ACh inhibited the 5-HT binding but NA had no effect. A double reciprocal plot of 5-HT binding represented a multiple binding mode, not a straight line. This observation suggested that, at least, three binding components (or sites) are implicated in the binding of 14C . 5-HT to this recombinate system having 3 Kds of 2.2 x 10(-7), 4.1 x 10(-7) and 4.2 x 10(-6) m. All these observations infer that the 5-HT binding components of myelin proteolipids are mainly three acidic lipids in nature.