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Thermotropic lipid phase separations in human platelet and rat liver plasma membranes (1983)

Gordon, Larry M. ; Mobley, Patrick W. ; Esgate, Judy A. ; [et al.]

Springer

The journal of membrane biology 76 (1983), S. 139-149

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ISSN: 1432-1424

Keywords: platelet plasma membranes ; liver plasma membranes ; spin probe ; cholesterol ; lipid phase separation ; platelet acid phosphatase

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Chemistry and Pharmacology

Notes: Summary Electron spin resonance (ESR) studies were conducted on human platelet plasma membranes using 5-nitroxide stearate, I(12,3). The polarity-corrected order parameterS and polarity-uncorrected order parametersS(T ‖) andS(T ⊥) were independent of probe concentration at low I(12,3)/membrane protein ratios. At higher ratios,S andS(T ⊥) decreased with increasing probe concentration whileS(T ‖) remained unchanged. This is the result of enhanced radical interactions due to probe clustering. A lipid phase separation occurs in platelet membranes that segregates I(12,3) for temperatures less than 37°C. As Arrhenius plots of platelet acid phosphatase activity exhibit a break at 35 to 36°C, this enzyme activity may be influenced by the above phase separation. Similar experiments were performed on native [cholesterol/phospholipid ratio (C/P)=0.71] and cholesterol-enriched [C/P=0.85] rat liver plasma membranes. At 36°C, cholesterol loading reduces I(12,3) flexibility and decreases the probe ratio at which radical interactions are apparent. The latter effects are attributed to the formation of cholesterol-rich lipid domains, and to the inability of I(12,3) to partition into these domains because of steric hinderance. Cholesterol enrichment increases both the high temperature onset of the phase separation occurring in liver membranes from 28° to 37°C and the percentage of probe-excluding, cholesterolrich lipid domains at elevated temperatures. A model is discussed attributing the lipid phase separation in native liver plasma membranes to cholesterol-rich and-poor domains. As I(12,3) behaves similarly in cholesterol-enriched liver and human platelet plasma membranes, cholesterol-rich and-poor domains probably exist in both systems at physiologic temperatures.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02000614

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Spin label studies on rat liver and heart plasma membranes: Effects of temperature, calcium, and lanthanum on membrane fluidity (1978)

Gordon, Larry M. ; Sauerheber, Richard D. ; Esgate, Judy A.

New York, N.Y. : Wiley-Blackwell

Journal of Supramolecular Structure 9 (1978), S. 299-326

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ISSN: 0091-7419

Keywords: lanthanum ; calcium ; lipid phase separation ; lipid clusters ; spin label method ; membrane fluidity ; temperature ; Life Sciences ; Molecular Cell Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: The structures of rat liver and heart plasma membranes were studied with the 5-nitroxide stearic acid spin probe, I(1 2,3). The polarity-corrected order parameters (S) of liver and heart plasma membranes were independent of probe concentration only if experimentally determined low I(1 2,3)/lipid ratios were employed. At higher probe/lipid ratios, the order parameters of both membrane systems decreased with increasing probe concentration, and these effects were attributed to enhanced nitroxide radical interactions. Examination of the temperature dependence of approximate and polarity-corrected order parameters indicated that lipid phase separations occur in liver (between 19° and 28°C) and heart (between 21° and 32°C) plasma membranes. The possibility that a wide variety of membrane-associated functions may be influenced by these thermotropic phase separations is considered.Addition of 3.9 mM CaCl2 to I(1 2,3)-labeled liver plasma membrane decreased the fluidity as indicated by a 5% increase in S at 37°C. Similarly, titrating I(1 2,3)-labeled heart plasma membranes with either CaCl2 or LaCl3 decreased the lipid fluidity at 37°C, although the magnitude of the La3+ effect was larger and occurred at lower concentrations than that induced by Ca2+; addition of 0.2 mM La3+ or 3.2 mM Ca2+ increased S by approximately 7% and 5%, respectively. The above cation effects reflected only alterations in the membrane fluidity and were not due to changes in probe-probe interactions. Ca2+ and La3+ at these concentrations decrease the activities of such plasma membrane enzymes as Na+, K+-ATPase and adenylyl cyclase, and it is suggested that the inhibition of these enzymes may be due in part to cation-mediated decreases in the lipid fluidity.

Additional Material: 6 Ill.