The early embryo membrane is highly permeable for water. Itmakes the cell very sensitive to osmotic shock. The cell volume alteration plays an important role in regulation of key cellular functions, including metabolism, protein synthesis, gene expression, proliferation and cell death. A fundamental property of animal cells is the ability to regulate their own volume. Even under hypotonic stress the cells can readjust their volume after transient osmotic swelling by a mechanism known as regulatory volume decrease (RVD). The nature of the regulatory mechanisms governing the volume changes in embryonic cell during RVD is not clear.

Osmotic adaptation in a blastomere of two-cell mouse embryo has been studied employing the direct measurement of cell volume with laser scanning microscopy followed by three-dimensional reconstruction. The hypotonicity was created by replacing 140mM NaCl in Dulbecco`s solution with 70mM NaCl. The keeping of the intact volume of the embryo compartments was based on freeze-drying technique. A Z-stack of optical slices was obtained in a confocal microscope (Zeiss, Germany). 3-DR was performed in the 3ds max medium.

Our data indicate that a long-term hypoosmotic shock results in the embryo volume recovery. Exposure of embryonic cells to the hypotonic K⁺-free medium does not influence on the kinetics of cell osmotic behavior. Blastomere's volume recovery is abolished after incubation in hypotonic Dulbecco`s with Cytochalasin B.

Na⁺ /K⁺ -ATPase inhibition does not influence on RVD of the embryonic cells, but volume recovery specific for hypotonic shock is blocked by the alteration of F-actin organization.