The influence of diffusion in the external medium upon the determination of cytoplasmic diffusion coefficients

The exchange of isotopic water has been studied in ovarian eggs from three Anuran species (R. esculenta, R. pipiens and R. temporaria) by the automatic diver balance technique. The oocytes were treated with chemicals (digitonin, ethanol and formaldehyde) to remove the plasma membrane. The cytoplasmic diffusion coefficient for water was calculated with and without allowance for the influence of diffusion in the external medium. The former expedient was found necessary in order to obtain correct values. The chemical treatments gave different values, but there are sound reasons to believe that those obtained with digitonin (8.9, 15.3 and 10.8.10−6 cm2sec−1 for R. esculenta, R. pipiens and R. temporaria, respectively) are the correct ones. These results indicate that the rate of diffusion in the oocyte cytoplasm amounts to 50–75% of that of free diffusion.