In pulmonary surfactant (PS) the coexistence of the ordered (Lo) and disordered (Ld) lipid phases would be essential for an optimal activity. Electron spin resonance (ESR) of PS labeled with 5-doxil stearic acid shows two spectral components called S and W. S/W ratio could be understood as the ratio between the probe population in Lo and in Ld. Although the specificity of S/W as an indicator of Lo/Ld has not yet been demonstrated, S/W has been used qualitatively to study changes in Lo/Ld. The goal of this paper is to stablish the correlation between S/W parameter and the amount of lipids in Ld (%Ld) measured by the ESR TEMPO technique described in our previous work. S/W and %Ld were measured in different PS samples under different experimental conditions. The results showed an inverse correlation between S/W and %Ld (r = -0.983; p < 0.001). We demonstrated that the S/W is sensible to the changes of Lo/Ld and can be used to quantify the %Ld.
Keywords: %Ld; 5DSA; ESR; Lipid phases; Pulmonary surfactant.
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