Block I, Wolke A, Briegleb W, Ivanova K
DLR (German Aerospace Establishment) Institute of Aerospace Medicine, Department of Biology, Cologne, Germany.
Acta Astronaut. 1995 Oct-Dec;36(8-12):479-86. doi: 10.1016/0094-5765(95)00134-4.
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.
多细胞生物以及单细胞生物中的细胞信号处理，必须依赖于基本相似的机制。自由生活的单细胞通常利用重力矢量进行空间定向（趋重力性），并表现出明显的重力敏感性。在本研究中，使用了对重力敏感的大型变形虫状细胞多头绒泡菌（黏菌门，非细胞黏菌）。在180度旋转实验以及模拟和实际的微重力研究（快速旋转回转器；空间实验室D1、IML-1）中，证明了其趋重力性以及重力对其固有节律性收缩活动的调节。在IML-2实验中研究了刺激感知，该实验通过测定细胞的加速度敏感性阈值，提供了有关重力感受器本身的信息。旨在阐明导致运动反应的信号转导后续步骤的地面实验表明，加速度刺激会引起第二信使3',5'-环磷酸腺苷（cAMP）水平的变化，这也表明多头绒泡菌的加速度刺激信号转导链使用了一种普遍存在的第二信使途径。
