Short-term microgravity to isolate graviperception in cells.

In the fall of 1991 a series of drop-tower experiments in ZARM (Bremen) was devoted to behavioural responses of unicellular organisms to step-type transition from normal gravity to microgravity. Modules for simultaneous 4-fold video-recording were incorporated into the flight capsule. In the course of 25 flights, 100 sets of experiments, each holding 100 to 200 cells, were flown under various conditions with a technical success rate of 94% and about 80% of the cells accessible to evaluation in the laboratory. A major goal of the experiments was the assessment of parameters of locomotion (velocity, orientation) in the absence of the gravity vector. The data show that in two species, Paramecium and Loxodes, the properties of steady-state microgravity-swimming correspond to horizontal swimming under 1g-conditions. In a third species, Didinium, microgravity-swimming velocity exceeds 1 g-horizontal rates. The data are in agreement with an electrophysiological hypothesis of graviperception in cells.