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At least 883 records · Page 49Linked to original sources
PubMed1982

The relationship between plasma membrane lipid composition and physical-chemical properties. III. Detailed physical and biochemical analysis of fatty acid-substituted EL4 plasma membranes.

Murine leukemia EL4 cells were modified by supplementation of culture media with fatty acids for 24 h. A plasma membrane-enriched fraction was prepared from substituted and normal cells. Analyses were performed to determine fatty acyl composition, phospholipid headgroup composition and cholesterol content. The two major membrane phospholipids, phosphatidylethanolamine (PE) and phosphatidylcholine (PC) were isolated by thin-layer chromatography and ESR measurements were done on liposomes prepared from these lipids as well as on the intact plasma membrane preparations. Slight perturbations in overall plasma membrane lipid composition were observed when EL4 cells were supplemented with a single exogenous fatty acid. This may be consistent with the idea that the incorporation of exogenous fatty acid induces compensatory changes in membrane lipid composition. On the other hand, we observed no significant difference in two ESR motional parameters between the unsubstituted control and various fatty acid-substituted plasma membranes. ESR measurements carried out on PE and PC liposomes derived from 17:0- and 18:2c-substituted membranes also failed to detect major differences between these liposomes and those made from normal EL4 phospholipids. In the case of liposomes prepared from 18:2t,-substituted membranes, the order parameter was significantly changed from the normal. However, the change was in opposite directions in PE and PC, perhaps accounting for the fact that no change parameter is seen in intact 18:2t-substituted plasma membrane. Measurements of order parameter (S) in mixed lipid vesicles showed that at up to 50 mol% mixture of a synthetic PC with plasma membrane PC, the value of S was only marginally different from that of the plasma membrane PC vesicles. We interpret these data as an indication that the two ESR parameters used are not sufficiently sensitive to detect changes due to modifications of the acyl chain composition of a complex biological membrane.

Animals↗
PubMedDate not supplied

Towards physical dynamic tolerance: an approach to resolve the conflict between free will and physical determinism.

This paper attempts to resolve the conflict between free will and determinism. The problem is approached by demonstrating that: (a) some well-established experimental observations indicate that irreversibility persists at the molecular level, (b) microscopic reversibility is not fully compatible with macroscopic irreversibility, (c) an overall consistency can be maintained if microscopic reversibility is regarded only as an excellent approximation, whereas microscopic irreversibility together with chaos can account for macroscopic reversibility, and (d) endogenous noise serves a vital function of nerve excitation. Thus, the mean of position and momentum specified by a non-deterministic law of motion gives the law its superficially deterministic behavior and predictability, whereas its dispersion grants dynamic tolerance and irreversibility. Therefore, causality is preserved while a limited degree of freedom allows for the exercise of free will. However, it is argued that free will can never be proven or disproven by a conventional behavioral experiment.

Conflict, Psychological↗