The effects of gravity on alamethicin doped planar lipid bilayers and on reconstituted porins of Escherichia coli outer membrane, respectively, have been investigated in this paper. The aim of the study was to find out whether and how gravity influences the highly stratified system: membrane-ion channel, in order to provide a novel approach to the explanation of gravity effects on living systems. This is necessary, as even single cells can react to gravity changes without having perceptive organelles. The mechanism of this detection is not clear yet. One possibility might be the detection of gravity by the membrane itself, or by the interaction of integral membrane proteins with gravity. Here we show for the first time that gravity directly influences the integral open state probability of native ion channels (porins) incorporated into planar lipid bilayers. Under hypergravity, especially the open state probability of porins is increased, whereas it is decreased in the microgravity case. The dependency is sigmoidal with the steepest region at 1 to 1.3 g. In the light of these experiments, a general effect of gravity on ion channels and membranes seems to be reasonable, possibly providing an explanation for several impacts of gravity on living systems.
The onset and propagation of waves in an excitable medium were investigated using the retinal Spreading Depression (rSD). The rSD is an ideal tool for this purpose. The retina of chicken, which was used in all experiments, is a close to two-dimensional system, in which the wave can easily be observed by optical techniques in time and space. rSD waves can be elicited by a variety of stimuli. Between stimulus and onset of the wave a temporal delay is always present. We found that the wave velocity is a function of the duration of this delay. In this paper we show, that within this time increasing fluctuations occur of system parameters.Another set of experiments deals with spatial correlations in the rSD. In some experiments we found the onset of the wave to be about 300 µm locally displaced with respect to the point of stimulus.In collision experiments, the spread velocity of two wavefronts approaching each other was measured. We found a significant increase in the velocity. This increase in velocity takes place on the last 250 µm before collision. This distance resembles the one found for local displacements, indicating a common origin.
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