Paramecia and Gravitation

Many protozoans have to swim harder going up than going down, just to keep from sinking.

Physicists Karine Guevorkian and James Valles of Brown University wanted to see how creatures like paramecia respond at an up side down gravity. They put a tube with water containing live paramecia inside a high-powered electromagnet at the National High Magnetic Field Laboratory in Tallahassee, Florida. The organisms are less susceptible to a magnetic field than plain water is. The magnetic field generated inside the tube "pulls" harder on the water than on the cells. Down pulling fields maintain the cells floating, up pulling fields sink the cells. With pure water, the effect of gravity increased by about 50 percent. They added to the water a compound called Gadolinium-diethylene-triamine-pentaacetate (Gd-DTPA), which is highly susceptible to induced magnetic fields such as those generated in electromagnets.

The water was much "heavier" or "lighter", relative to the paramecia, to an effect up to 10 times that of normal gravity. Because magnetic field could be continuously adjusted, the researchers could create conditions simulating zero-gravity and inverse-gravity. Simulating "heavier" or "lighter" water, the researchers could dramatically change the swimming behavior of the paramecia.

In high gravity, the organisms swam upward mightily to maintain their place in the water column. In zero gravity, they swam up and down equally. And in reverse gravity, they dove for where the sediments ought to be. "If you want to make something float more," said Valles, "you put it in a fluid and you pull the fluid down harder than you pull the thing down. And that's what we basically do with the magnet. That causes the cell to float more - and that turns gravity upside down for the cell."

The team tested the limits of protozoan endurance. At about eight times normal gravity, the paramecia swam upward, but not progressing. They measured the force needed to counter the gravitational effect: 0.7 nano-Newtons. In comparison, the force required to press a key on a computer keyboard is about 22 Newtons (3 billion times as strong).

Spatial research presented many biological problems induced by reduced gravity, such as changes in bone cell development and gene expression. Methods for manipulating gravity in the Earth-based laboratory have been few and troublesome, asking further research in these areas.

This method will allow researchers to put small biological systems to gravitational effects, like to those encountered in space, allowing less expensive and more complex experiments.