title: Gravity perception and signal transduction in single cells.
abstract: Cellular signal processing in multi-, as well as in unicellular organisms, has to rely on fundamentally similar mechanisms. Free-living single cells often use the gravity vector for their spatial orientation (gravitaxis) and show distinct gravisensitivities. In this investigation the gravisensitive giant ameboid cell Physarum polycephalum (Myxomycetes, acellular slime molds) is used. Its gravitaxis and the modulation of its intrinsic rhythmic contraction activity by gravity was demonstrated in 180 degrees-turn experiments and in simulated, as well as in actual, near-weightlessness studies (fast-rotating clinostat; Spacelab D1, IML-1). The stimulus perception was addressed in an IML-2 experiment, which provided information on the gravireceptor itself by the determination of the cell's acceleration-sensitivity threshold. Ground-based experiments designed to elucidate the subsequent steps in signal transduction leading to a motor response, suggest that an acceleration stimulus induces changes in the level of second messenger, adenosine 3',5'-cyclic monophosphate (cAMP), indicating also that the acceleration-stimulus signal transduction chain of Physarum uses an ubiquitous second messenger pathway.
authors.affiliation: DLR (German Aerospace Establishment) Institute of Aerospace Medicine, Department of Biology, Cologne, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Block
authors.forename: A
authors.initials: A
authors.lastname: Wolke
authors.forename: W
authors.initials: W
authors.lastname: Briegleb
authors.forename: K
authors.initials: K
authors.lastname: Ivanova
mesh_terms: D000054:Acceleration; D000818:Animals; D002498:Centrifugation / Q000295:instrumentation; D000242:Cyclic AMP / Q000502:physiology*; D006112:Gravitation; D018466:Gravity Sensing / Q000502:physiology*; D008853:Microscopy / Q000295:instrumentation; D010804:Physarum; D012399:Rotation; D015290:Second Messenger Systems; D015398:Signal Transduction / Q000502:physiology*; D013026:Space Flight; D014893:Weightlessness; D018474:Weightlessness Simulation
chemical_list: D000242:Cyclic AMP