Theory of Domain Formation on Model Myelin Monolayer System

Lipid domains indicate the coexistence of thermodynamic phases of lipid molecules at hydrophobic-hydrophilic interface. Domain size, shape and distribution are directly affected by the line tension (λ) and dipole density difference (m) at domain boundaries [1-2]. In this work, a thermodynamic equation expressing domain size distribution was derived and fitted to domain distributions from fluorescence images of both healthy (control) and experimental allergic encephalomyelitis (EAE) cytoplasmic (CYT) model myelin monolayers. From these fits we simultaneously extract λ (in units of fN) and m (in units of pC/m2). Both parameters λ and m decrease with increasing surface pressure (Π). Moreover, the control monolayer had higher values of λ and m compare with EAE monolayer for all values of Π where domains can be observed clearly. Based on the difference of these values, EAE monolayer seems to be more ‘stressed’ than control monolayer. This indicates an important relationship between Π, domain size and distribution, λ and m, which can be used to point out the potential cause of demyelinating diseases like Multiple Sclerosis (MS) at molecular scale.