Studies of effects of flunitrazepam on the lamellar-hexagonal II phase transition of phosphatidyl-ethanolamine. Use of merocyanine 540 as a fluorescent indicator

GARCIA DA; PERILLO MA,

Bariloche

Congreso; XXXII Reunión Anual de la Sociedad Argentina de Biofísica; 2003

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman";} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Flunitrazepam (FNT) is an extensively used benzodiazepine (BZD) due to its potent anxiolytic and hypnotic action. Previous studies of our group demonstrated that BZD-membrane interaction could be explained by a partition equilibrium model. We showed that BZD partitioning in the membrane increased in quantity and depth as the membrane structural order decreased. Moreover, the localization of BZDs at the phospholipid polar head region could explain the decrease in the size of dpPC vesicles, through a mechanism that involves the increment in the relative volume of this polar head region inducing an increase in the vesicle’s surface curvature. In the present work we studied if FNT can affect the lamellar-hexagonal II phase transition of phosphatidyl ethanolamine through a similar mechanism. This study was approached by using the fluorescent dye merocyanine 540 which is sensitive to the molecular packing of membrane lipids. A detailed analysis of the effects of FNT on merocyanine absorption, fluorescence emission and excitation spectra, was performed. The results indicated that merocyanine behaved as a good indicator of this phase transition as was previously described. FNT did not affect the transition temperature but showed a tendency to diminish the dye fluorescence emission intensity which could involve topological changes leading to modifications in the polarity of the region sensed by merocyanine.