Experiment

Pikaru：

Hello, Doctor. Astronaut Wakata has left Earth for space for a long stay. I heard that astronauts do a lot of exercise in space to prevent muscle loss.

Doctor：

That’s right. Astronauts staying on a space station spend two hours a day exercising.

Pikaru：

Why do muscles weaken in space?

Doctor：

Mmm? You’ve forgotten what you learned before. I think you said “I understand this well, Doctor,” when you interviewed me about the Hybrid Training experiment and the Myo Lab experiment.

Pikaru：

I’m sorry, Doctor. I must have forgotten it because I’m growing so fast!

Doctor：

Muscles strengthen with training, and they weaken if they are not used. On Earth, you unconsciously use your muscles to support your body because gravitational force is always being applied.

Pikaru：

I see. We use our muscles unconsciously on Earth when we are just standing.

Doctor：

That’s right. When considered at the molecular level, this loss of muscle mass occurs because breakdown of muscle proteins surpasses production of muscle proteins in space. The Myo Lab experiment confirmed the mechanism of muscle atrophy in space.

Pikaru：

Really? But, to begin with, how do muscles know whether they are in space or on Earth?

Doctor：

That’s a very good question, Pikaru. We humans recognize which direction is up and which is down via signals from our eyes and organs in our ears. In fact, the human body consists of about 60 trillion cells, and each individual cell is affected by gravity and is said to be able to sense the presence or absence of the gravity. However, no one has attempted to confirm whether this is true or not.

Pikaru：

Individual cells sensing gravity... I have a feeling that I’ve heard of an experiment like this on plants.

Doctor：

That’s the Resist Tubule experiment. In plants, cell membrane deformation caused by the presence or absence of gravity is sensed by mechanoreceptors. Professor Sokabe thinks a more detailed mechanism allows animal cells to sense gravity.

Pikaru：

Please tell me about it, Doctor!

Doctor：

OK. Many flexible wire-like structures stretch through a cell and are connected to the cell membrane. Organelles such as nuclei and mitochondria, which are heavy and have a high specific gravity, are attached to the wires. In microgravity conditions, mitochondria float upwards, and the weight of the mitochondria disappears from the wires. The wires lose tension, and the membranes also loosen.

Pikaru：

I can see it!

Doctor：

The action of various channels (holes in the membrane surrounding the cell) is thought to change according to loosening of the cell membrane. But no one has tested this hypothesis at the cellular level.

Pikaru：

So it will be investigated in space?

Doctor：

Yes. Cell proteins will be fluorescently tagged and will be observed with a state-of-the-art microscope. In addition to investigating how cells, including muscle cells, sense gravity, measures against muscle atrophy will be examined. Candidate drugs for muscle atrophy, selected on the basis of the results of the Myo Lab experiment, will be administered to cells, and their effects on muscle cells in space will be examined.

Pikaru：

That’s why Professor Nikawa of the Myo Lab experiment is on the list of collaborating researchers. Will the cells return to Earth?

Doctor：

Yes, because in addition to observing the cells in space, the scientists will compare gene expression in the cells. The cells will be treated with a reagent to preserve genes, frozen, and returned to Earth. A small freezer, which can be taken in a spacecraft, is being prepared.

Pikaru：

I’m looking forward to seeing the results of this experiment! I hope this experiment and the results contribute to the development of medicines for muscle weakening, not only for astronauts but also for bedridden people. Thank you very much for the explanation, Doctor.