Comparison of steady-state fluorescence polarization and urea permeability of phosphatidylcholine and phosphatidylsulfocholine liposomes as a function of sterol structure

✍ Scribed by E.L. Pugh; R. Bittman; L. Fugler; M. Kates

• Publisher: Elsevier Science
• Year: 1989
• Tongue: English
• Weight: 567 KB
• Volume: 50
• Category: Article
• ISSN: 0009-3084
• DOI: 10.1016/0009-3084(89)90024-8

✦ Synopsis

The well-known reduction in the permeability properties of liposomes of dimyristoylphosphatidylcholine (DMPC) by sterols has also been demonstrated for its sulfonium analog (DMPSC) in which the N+(CH3)3 group of choline is replaced by S+(CH3)2. We have now compared the effects of 25 tool% 24-methylenecholesterol and cholesterol on the initial rates of urea permeation into dipalmitoyl-PC (DPPC) and dipalmitoyi-PSC (DPPSC) liposomes above the gel-to-liquid-crystalline phase transition temperature and found a greater reduction with 24-methylenecholesterol/DPPSC than with cholesterol/DPPSC liposomes but little difference between the two sterols in DPPC liposomes. Fluorescence polarization studies, using diphenylhexatriene as a probe, show that polarization (P) values are considerably higher in DMPSC liposomes containing 20 and 30 tool% 24-methylenecholesterol than in DMPC liposomes containing 20 and 30 tool% cholesterol. Higher P values were also obtained in DMPSC liposomes containing other 24-alkyl-substituted sterols (fl-sitosterol, ergosterol and campesterol) than in DMPC liposomes containing the same sterols. Reduced permeability rates in PSC liposomes containing 24-alkyl-substituted sterols are correlated with higher polarization values, reflecting an increased degree of order and/or motion in these liposomes compared with liposomes from the corresponding PC. These results suggest that alkyl substitution at C-24 of the sterol molecule results in tighter interactions with the sulfonium analog of PC than with PC.