Comparison of Triton X-100 Penetration into Phosphatidylcholine and Sphingomyelin Mono- and Bilayers

Abstract

This study has addressed the question whether there is a difference in resistance to Triton X-100 penetration of sphingomyelin and phosphatidylcholine membranes. We have studied this by measuring the penetration of Triton X-100 into monolayers of either D-erythro-N-palmitoylsphingomyelin or dipalmitoylphosphatidylcholine (DPPC) at constant lateral surface pressure and 22 °C. In addition, we also compared how Triton X-100 penetrated into egg phosphatidylcholine and D-erythro-24:1 ∆15c sphingomyelin monolayers and how the presence of cholesterol affected the penetration process. In bilayer membranes we assessed Triton X-100 insertion and solubilization by studying the thermodynamics of the partition process and determining the detergent:ratio at which the solubilization is initialized. The penetration of Triton X-100 from the subphase into the monolayers was concentration and surface pressure dependent. The penetration increased linearly with time and concentration for DPPC monolayers, but with sphingomyelin monolayers, the response was clearly biphasic and faster. If the penetration was allowed to proceed, the monolayers eventually became unstable and collapsed (at collapse the detergentto-lipid ratio was about 1:4 in the monolayer). Inclusion of 30 mol % cholesterol in the monolayers made them more resistant to Triton X-100 penetration, irrespective of the host phospholipid type. In bilayers the partition coefficient (K) becomes lower and the enthalpy change (∆H) higher for partitioning of Triton X-100 into D-erythro-N-palmitoylsphingomyelin as compared to into DPPC. Onset of solubilization was reached at lower detergent:lipid ratios in D-erythro-N-palmitoylsphingomyelin than in DPPC vesicles. In conclusion, we have observed that D-erythro-N-palmitoylsphingomyelin monolayers do not show increased resistance toward Triton X-100 penetration as compared with membranes prepared from an acyl-matched glycerophospholipid, at least not at room temperature and not even when cholesterol is present. Sphingomyelin bilayers are more susceptible to Triton X-100 solubilization than phosphatidylcholine bilayers, although K was lower for Triton X-100 into sphingomyelin bilayers.

Triton X-100 concentration effects on membrane permeability of a single HeLa cell by scanning electrochemical microscopy (SECM)

“…The insertion of individual detergent molecules or small aggregates at concentrations just below the CMC causes the membrane to become more permeable to a wide variety of molecules which otherwise cannot enter inside the cell allowing transfection. However at detergent concentrations where micelles form (at or above the CMC range), rapid breakdown of the membrane occur (11,(28)(29)(30)(31).…”

“…Moreover, cholesterol or similar molecule-rich membrane domains are reported to be more tolerant toward detergents such as TX100 molecules in comparison to other parts of the lipid bilayer. (8)(9)(10)(11)(12)(13)(14).…”

Plasma membrane rafts of rainbow trout are subject to thermal acclimation

“…The capacity of a membrane to incorporate detergent monomers is inversely proportional to the lipid-lipid interaction strength in the membrane (Lichtenberg et al, 1979). For example, a Langmuir trough study demonstrated that small increases in lateral pressure, with concomitant increases in lipid cohesion forces, resulted in large decreases in the incorporation of Triton X-100 (Nyholm and Slotte, 2001).…”

Lipid Dynamics and Domain Formation in Model Membranes Composed of Ternary Mixtures of Unsaturated and Saturated Phosphatidylcholines and Cholesterol

“…Conventional techniques, e.g., the test for detergent insolubility, have often been used in the past to reveal rafts in vitro and in vivo. However, they did not show considerable differences between sphingomyelin-and saturated glycerophospholipid (i.e., DPPC) liquid-ordered phases (Ahmed et al, 1997;Nyholm and Slotte, 2001). Recent advances in confocal optical microscopy have supported the direct visualization of raft-assembly in supported planar membranes (Dietrich et al, 2001a,b) and giant unilamellar vesicles (GUVs) (Bagatolli and Gratton, 2000;Kahya et al, 2003).…”