The role of cytoplasmic membranes in the regulation of water concentration within frog oocytes

Abstract

Large ovarian oocytes from frog ovaries were treated for 1 sec in water of 80°C. Such “nudoplasts” were shown to lose ultraviolet-absorbing and trichloroacetic acid-precipitable substances into a physiological saline medium. They were also shown to be permeable to labeled gamma globulin protein and to be unable to retain their normal appearance. Despite the fact that they had become highly permeable, nudoplasts could still change volume in hyper- and hypotonic salt solutions for a period of one to several hours. They could swell markedly in hypotonic media but sometimes could not shrink in hypertonic salt solutions. These data were interpreted as evidence that the oocytes consist of two osmotically active “compartments”. One, the protoplasmic mass, owing its osmotic properties to the plasma membrane and the other consisting of interior vesicles owing their osmotic properties to their investing membranes. In nudoplasts the surface damage renders the protoplasmic compartment osmotically non-functional but the vesicular compartment is though to retain its osmotic properties. Cytological evidence of swollen cortical vesicles in normal cells was presented to support the argument. Examination of the magnitude of swelling led to the conclusion that the interior vesicles could not increase in volume to the observed extent simply with semi-permeable membranes and a fixed solute content. It was suggested that ion-pumping takes place into the vesicles of the cytoplasm, especially those of the cell cortex.