Abstract
Biological membranes are preferentially composed of lipids and proteins, and it is assumed that mainly the proteins are responsible for their functional properties. Nevertheless, during the last years, the contribution of the plain lipid matrix and its physico-chemical parameters to membrane functionality has been shown to be of high relevance. This is also correct for the gravity dependence of cells and organisms which is well accepted since long for a wide range of biological systems. Thus, the question must be asked, whether, and how far plain lipid membranes are affected by gravity directly. In this study we show that the fluidity (viscosity) of plain lipid membranes, as well as that of cell membranes, is gravity dependent, using a multipurpose 96-well plate reader in the fluorescence polarization anisotropy mode in a parabolic flight mission. Plain lipid vesicles and cells from a human cancer cell line have been used in these experiments. Necessarily, membrane-integrated proteins should be affected by this in their function. As a consequence any living cell will be able to sense at least basically gravity.
Highlights
Biological membranes are preferentially composed of lipids and proteins, and it is assumed that mainly the proteins are responsible for their functional properties, and for a possible gravity dependence
The duration of the microgravity and macro gravity phases are in the range of 20 seconds, the 1 g phases last from 1 acceleration [g]
In a first set of experiments we investigated the influence of gravity on the membrane fluidity of Asolectin vesicles at a temperature around 23 ̊C using fluorescence polarization (FP) of DPH
Summary
Gravity is known to influence a lot of physical and biological processes. Biological cells and their reactions are no exception. In previous studies additional results have been obtained for different ion channels, which show a changed activity under microgravity [2]-[4]. Such changes in ion-channel activity might be well responsible for changes in higher cellular function. A change, for example, in membrane fluidity could result in the change of function of ion-channels. The same would be true for the function of all other integral membrane proteins under conditions of variable gravity
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