Hydrostatic pressure reversibly blocks membrane control of ciliary motility in Paramecium.

A hydrostatic pressure of only 68 atmospheres prevented swimming Paramecium caudatum from "avoiding" or reversing direction; 170 atmospheres stopped or decreased forward velocity by more than 75 percent. A decompression of 40 atmospheres invoked a single reversal, even at ,80 atmospheres. In contrast, 170 atmospheres did not significantly affect swimming behavior of paramecium "models" that were reactivated in a solution containing adenosine triphosphate and magnesium ions after their membrane had been disrupted by Triton X-100.