Thermal response of domains in cardiolipin content bilayers

In the study described here, supported planar bilayers (SPBs) of 1-palmitoy-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE):cardiolipin (CL) (0.8:0.2, mol/mol) were examined using atomic force microscopy (AFM). SPBs were formed from suspensions of POPE:CL (0.8:0.2, mol/mol) in inverted hexagonal (HII) phases (buffer containing Ca2+). Three laterally segregated domains which differ in height were observed at 24 °C. Based on the area accounted for each domain and the nominal composition of the mixture, we interpret that the higher domain is formed by CL, while the intermediate and lower domains (LDs) are formed by POPE. The three domains respond to temperature increase with relative changes in their area. At 37 °C, we observed that the increase in the area of the intermediate domain occurs at the expense of the LD. 31P-nuclear magnetic resonance (31P-NMR) and Differential scanning calorimetry (DSC) were used in combination with AFM to characterize the phase behavior of the suspensions and to elucidate the nature of the structures observed.