Effect of gangliosides on phospholipid bilayers: a study with the lipophilic ions relaxation method

The presence of monosialoganglioside GM1 in dioleoylphosphatidylcholine black lipid membranes modifies the transport properties of the hydrophobic ion tetraphenylborate and the kinetics of relaxation of this ion after the application of a voltage step. At zero applied voltage, the difference in the relaxation time constants between pure phospholipid and ganglioside-phospholipid mixed membranes is large. This difference may possibly rise from changes in the membranes fluidity since it has been found that the two types of membranes do not show appreciable difference in thickness. A uniform distribution of GM1 in the membrane seems to be more probable than the presence of lateral phase separation phenomena. The partition coefficient of tetraphenylborate between the bathing NaCl solution and the membrane appears to depend on the ionic strength, which controls the screening effect of the Na+ ions on the COO- charged groups of the sialic acid of the ganglioside polar heads. Effects of dipolar potentials on the partition coefficient can be excluded, being the absorption plane of tetraphenylborate probably located outside the dipolar layer of the membrane.