High Hydrostatic Pressure Effects on Amoeba Proteus

Upon application of hydrostatic pressure to Amoeba proteus, all movement stops and the organism assumes a spherical shape (1). The attainment of a completely spherical shape is a gradual process requiring from 5 to 20 minutes, depending upon the pressure and temperature level. This "spher-ing" under pressure has been attributed to the reversible disruption of the plasmagel integrity and consequent loss of structural opposition to the tensional forces at the surface of the ameba. However, one of the initial events is the collapse of the contractile vacuole, and this has posed some questions as to the nature of the "sphering" phenomenon. The disruption of osmoregulation under pressure could result in swelling, with the final diameter of the sphere being determined by the eventual equilibration of the osmotic forces involved and the elastic tension of the membrane. Of further consideration is the fact that the sphere represents a minimal surface area for a given volume. Should there be no change (or even a slight decrease) in the volume of the organism during "sphering," a decrease in surface area must occur. Similarly, on release of pressure, as pseudopodial flow returns, an increase in surface area must occur. However, should there be some increase in volume due to osmosis, no change in surface area need occur since the sphere surface might then represent the minimal surface for an increased volume. While theoretical considerations of relative vapor pressures under conditions of high hydro-static pressure would seem to eliminate osmosis as an experimental factor, it was thought necessary to perform experiments concerned with actual volume changes in A. proteus during the period of pressure application. MATERIAL AND METHODS A. proteus were cultured in Chalklcy's medium and fed washed Tetrahymena pyriformis in accordance with the method of Griffin (2). In order to facilitate measurement of relative changes in volume, the amebas were entrapped in fine glass capillary tubes. The diameter of the capillary had to be large enough, however, to permit adequate frcc membrane surface for possible osmotic transfer of solvent. The pressure methods and equipment were similar to those previously described (1). A diagrammatic representation of the experimental apparatus is shown in Fig. 1. The specimen chamber is made by mounting two coverslips on either end of a glass ring rimmed with a moderately thick layer of stopcock grease. Several amebas suffered membrane damage while being sucked into the capillary tube. Upon observation in the …