Measurement of elastic properties of Xenopus oocytes

Elastic properties of Xenopus oocytes were examined by measuring intracellular pressure (Pic) and cell volume (Vc) in cells undergoing osmotic swelling. Pic was measured by micropuncture, using the servo-null technique. Vc was obtained by analyzing images acquired from a microscope having a video camera attachment. During osmotic swelling, Pic increased from 61 +/- 17 to 500 +/- 59 Pa (mean +/- SE), but the relationship with volume was not linear. In cells that underwent sequential swelling and shrinking, Pic was always lower on shrinking and the cells showed hysteresis. Cells with vitelline envelope (VE) removed had Pic-Vc curves similar in shape to those of intact cells; however, Pic values were significantly lower. Specific elastance[delta Pic/(delta Vc/Vc)] was reduced by removal of the VE. The data indicate that oocytes are weakly elastic and that a large part of their resistance to expansion resides in the VE.