Incorporation of biogenic amines into phospholipids studied in two-phase-system

Phospholipids (PL) from splenic nerves, splenic nerve granules, adrenal medullary granules and egg yolk were used as binding ligands for studies on uptake of various biogenic amines. Efficient uptake of catecholamine (CA) occurred at low ionic strength (about 2-5 mM) and at pH 6.8-7.7. This uptake was also a function of the amine concentration in the aqueous medium. At higher ionic strength (e.g. 128 mM K-phosphate buffer) an uptake still occurred, but to considerably less extent, apparently since the association/dissociation ability of the amines within the PL was a function of cation concentration in the aqueous media. Sucrose- and dextrose-induced increase in the osmolarity of the aqueous medium did not to any appreciable extent reduce the CA uptake. Scatchard plot indicated that only one type of binding sites was engaged when PL from splenic nerves was used. Using PL from splenic nerves the following affinity order was obtained for the amine tested: 5-HT greater than TA greater than DA greater than NA greater than IP greater than A. When PL from medullary granules was used the order was: DA greater than IP greater than A greater than or equal to NA. No or negligible uptake of Dopa and its metabolites Doma and Dopac occurred. When added to the aqueous medium, the cationic amphiphilic detergent CTAB induced some uptake of Doma and Dopac, but no a Dopa. However, CTAB considerably diminished the uptake of NA and the other amines. On the other hand, ionic (DOC) and anionic (SDS) detergents strongly increased the uptake of NA and other amines into PL. The nonionic Triton X-100 was without significant effect on uptake of NA. It is suggested that the binding ligands may be present in the dipolar head of the PL molecules, particularly in the lipid phosphate group. The lipid protein may also be partially involved since chromatographic experiments showed that the CA accompanied lipid phosphorus and lipid protein. Electrostatic or complex interaction of CA within the polar head group or in conjunction with lipid protein would constitute an amine storage with efficient association/dissociation capacity.