Membrane Properties of D-erythro-N-acyl Sphingomyelins and Their Corresponding Dihydro Species

Abstract

We have prepared acyl chain-defined D-erythro-sphingomyelins and D-erythro-dihydrosphingomyelins and compared their properties in monolayer and bilayer membranes. Surface pressure/molecular area isotherms of D-erythro-N-16:0-sphingomyelin (16:0-SM) and D-erythro-N-16:0-dihydrosphingomyelin (16:0-DHSM) show very similar packing properties, except that the expanded-to-condensed phase transition (crystallization) occurs at a lower surface pressure for 16:0-DHSM. The measured surface potential was generally about 100 mV less for 16:0-DHSM monolayers compared to 16:0-SM monolayers. The condensed domains (crystals) that formed in 16:0-SM monolayers as a function of compression displayed star-shaped morphology when viewed under an epifluorescence microscope. 16:0-DHSM monolayers did not form similar crystals upon compression. 16:0-DHSM was degraded much faster by sphingomyelinase from Staphylococcus aureus than 16:0-SM (10-fold difference in enzyme activity needed for comparable hydrolytic rate). Cholesterol desorption from 16:0-DHSM to cyclodextrin was slightly slower (approximately 20%) than the rate measured from 16:0-SM monolayers (at 60 mol % cholesterol). The bilayer melting temperature of 16:0-DHSM was 47.7 degrees C (DeltaH 8.3 kcal/mol) whereas it was 41.2 degrees C for 16:0-SM (DeltaH 8.1 kcal/mol). Cholesterol/16:0-DHSM bilayers (15 mol % sterol) had more condensed domains than comparable 16:0-SM bilayers, as evidenced from the quenching resistance of DPH in DHSM membranes. We conclude that cholesterol interacts more favorably with 16:0-DHSM and that the membranes are more condensed than comparable 16:0-SM-containing membranes.

Regulation of the Gating of BKCa Channel by Lipid Bilayer Thickness

“…The mean open time decreased from 25 to 11.3 ms (2-fold decrease), whereas the mean closed time increased almost 10-fold from 4.5 to 40.2 ms. We want to emphasize that although the spring model we applied here provides a simple and reasonable explanation for the increased activation of the BK channel in SPM membranes observed in this study, other mechanisms could contribute to the activation of the BK channel in SPM membranes, such as direct hydrogen-bonding interactions between SPM and BK Ca channel proteins. When compared with PCs, which have only hydrogen bond-accepting features (two ester carbonyls) in the interfacial region, SPM has amide and hydroxyl groups that can serve as hydrogen bond donors and acceptors; thus, SPM is capable of forming complex intermolecular hydrogen bonds with membrane proteins (60). Further investigations are under way in our laboratory to explore the potential activation of BK Ca channels in SPM membranes by direct hydrogen-bonding interactions between SPM and BK Ca channel proteins.…”

Sphingolipids in human lens membranes: an update on their composition and possible biological implications

“…DHSMs extracted from human lenses and dispersed in water, have a transition temperature T m of 43 • C, 9 • C higher than that for SMs from bovine brain (Borchman et al, 1996a). Studies of N-palmitoyl- DHSM,or DHSM(16:0), showed a T m of 47.7 • C, 6.5 • C higher than that of the corresponding unsaturated species SM(16:0) (Kuikka et al, 2001). In addition, the organogels formed by these PLs when dissolved in chloroform also exhibit different thermotropic properties.…”

“…The desorption rate of CHol was shown to be 20% slower in DHSM than in SM monolayers (Kuikka et al, 2001). Based on calorimetric and NMR spectral measurements (Epand, 2003), Epand also concluded that CHol can interact more favorably with bilayers of DHSMs than with those containing SMs, and that the fraction of miscible CHol is higher in bilayers of DHSMs.…”

“…Since DHSMs were identified as the major PL components in HLMs, two model studies have addressed and compared the interactions of CHol with SMs and DHSMs (Epand, 2003;Kuikka et al, 2001). The desorption rate of CHol was shown to be 20% slower in DHSM than in SM monolayers (Kuikka et al, 2001).…”

Lipids and the ocular lens

“…They are involved with cell signaling and endocytosis. Several reviews have focused on the function and the nature of the forces that lead to their formation (118)(119)(120)(121)(122)(123)(124)(125). Rafts have been reported in human lens membranes ( 34 ).…”