Monolayer coupling in phosphatidylserine bilayers: distinct phase transitions induced by magnesium interacting with one or both monolayers

We have investigated the thermotropic behavior of phospatidylserine bilayers interacting with Mg2+ either on one side or both sides, using differential scanning calorimetry. Large unilamellar vesicles (LUV) of phosphatidylserine exposed to Mg2+ on the external side only displayed an upward shift of the gel-liquid transition temperature (Tm) of about 6-8 degrees C relative to the Tm of LUV in Na+. Mg2+ was shown not to enter the vesicle interior, by means of fluorescence measurements on encapsulated 8-hydroxyquinoline-5-sulfonate. Multilamellar vesicles prepared in the presence of Mg2+, or vesicles prepared by Mg2+-induced fusion of small unilamellar vesicles, had Tm values that were shifted upward by about 16-17 C degrees. When the latter preparation was treated with EDTA to produce vesicles with Mg2+ inside and Na+ outside, the Tm was found to be shifted again by only 6-8 degrees C. These observations indicate that the monolayer interacting with Na+ fluidizes the monolayer interacting with Mg2+, and that the latter tends to solidify the former. The two monolayers thus appear to be coupled, possibly by hydrocarbon chain interdigitation.     

Modification of the structure of plasmatic membranes of the liver by the action of α-tocopherol in vitro

Biophysics - The effect of the natural antioxidant α-tocopherol in a broad concentration range (10?4–10?25 M) on the viscosity characteristics and thermally induced...     

Rapid miniaturization of Salvelinus fish as an adaptation to the volcanic impact

Hydrobiologia - Volcanoes serve as natural laboratories expanding our understanding of the recent and past ecological and evolutionary processes. Here, we present data elucidating the developmental...     

Nuclear organization studied with the help of a hypotonic shift: its use permits hydrophilic molecules to enter into living cells

A new procedure for introduction of hydrophilic molecules into living cells based on efficient uptake of these molecules into the cells during hypotonic treatment is presented and its use is demonstrated by a variety of applications. Experiments with cultured vertebrate and Drosophila cells and various animal tissues demonstrated that the increase in cell membrane permeability under hypotonic conditions is a general phenomenon in all animal cells tested. The efficiency of the method depends on the composition and temperature of the hypotonic buffer, the duration of the hypotonic treatment and the molecular weight of the molecules introduced into living cells. The versatility of this approach is demonstrated with various types of molecules such as modified nucleotides, nucleotides with conjugated fluorochrome, peptides, phosphatase substrates and fluorescent dyes. The method opens new possibilities for the direct investigation of a variety of biological problems as documented here with data on the functional organization of the cell nucleus. Received: 3 February 1999; in revised form: 18 June 1999 / Accepted: 18 June 1999