Interaction of ganglioside-containing planar bilayers with serotonin and inorganic cations

The binding of serotonin and inorganic cations K+, Na+, Ca2+, Mg2+ to planar bilayers formed from mixtures of phosphatidylcholine and mono-, di- and trisialogangliosides was studied by the potentiodynamic and nonactin-induced potassium conductivity method. The theoretical analysis of the results obtained was made taking into account (1) protrusion of the ganglioside charges from the membrane surface and (2) simultaneous adsorption of ions on the bilayer surface and on the ganglioside charges protruding into the solution. It was shown that there was no specific binding of K+ and Na+. The binding constants for Ca2+, Mg2+ were determined. These constants for all the gangliosides studied were equal to 500 M-1. The determined binding constants of serotonin to various gangliosides diminish in the following order: GD3 greater than GT1b greater than GD1a greater than GM1.