Oxygen transport parameter in membranes as deduced by saturation recovery measurements of spin-lattice relaxation times of spin labels.

Abstract

Spin-lattice relaxation time (T1) measurements of nitroxide radical spin labels in membranes have been made by using the saturation-recovery technique. Stearic acid and sterol-type labels were used as probes of dimyristoylphosphatidylcholine liposomes from 0 degrees C to 36 degrees C. In the absence of oxygen, the range of variation of T1 over all samples and conditions is about a factor of 3. Heisenberg exchange between oxygen and spin labels is an effective T1 mechanism for the spin labels. The full range of variation of T1 in the presence of air is about a factor of 100. It is suggested that the oxygen transport parameter W = T1(-1) (air) - T1(-1) (N2) is a useful new monitor of membrane fluidity that reports on translational diffusion of small molecules. The values of W change at the prephase and main phase transitions and vary in complex ways. Arguments are advanced that the data are indicative of anisotropic translational diffusion of oxygen.

Oxygen permeability of phosphatidylcholine--cholesterol membranes.

“…Using the theory of Diamond and Katz (7), we have assessed oxygen permeability across the membrane on the basis of W(x) profiles, assuming that oxygen diffusion is isotropic. We have previously shown that oxygen diffusion is almost isotropic in the liquid-crystalline phase of non-cholesterol-containing membranes (3). Diffusion of oxygen below the pretransition temperature was found to be more rapid in the transverse than in the lateral direction.…”

“…The buffer was 0.1 M borate at pH 9.5. To ensure that all probe carboxyl groups were ionized in PtdCho membranes, a rather high pH was chosen (3,5,12,13). The structure of PtdCho membranes is not altered at this pH (3,13).…”

“…Subczynski and Hyde (2) and Kusumi et al (3) observed oxygen transport in membranes using the electron spin-lattice relaxation time (T1) as a basic "clock." The rationale of the spin-label T1 method is that the molecular probe can be placed at a known location in the membrane to observe local events and that the time scale of T1 (1-20 ,u s) is in the correct range to study many molecular processes (4).…”

“…Between the pre-and maintransition temperature, our data with respect to the anisotropy of oxygen diffusion are complex and no detailed interpretation was advanced (3). Diamond and Katz (7) derived an expression for the permeability coefficient PM of a nonelectrolyte in terms of resistances r' and r" in the polar headgroup regions (8), the solute (local) partition coefficient K(x), and the solute (local) diffusion constant D(x), taking the plane of the membrane as perpendicular to the x axis: [3] The integration is taken across the hydrophobic portion ofthe membrane. Since a spin probe is placed in the polar regions as well as in the hydrophobic region in the present study, r' and r" can also be estimated within the integral.…”

Antioxidant properties of resveratrol and piceid on lipid peroxidation in micelles and monolamellar liposomes

“…Multilamellar vesicles were prepared following the method of Kusumi et al [26]. Phospholipids were dissolved in a 2:1 chloroform methanol mixture then dried with a stream of nitrogen gas and kept under vacuum for at least 14 h. The dried lipids were suspended, when not otherwise specified, in a HEPES 0.1 M, pH 7.2, buffer.…”