4. The intercellular fluid contains 100 mm sodium and 1 mM potassium; the majority of the sodium is ionically active. As no net uptake of sodium or potassium occurs before gastrulation these cations must have been transferred from the cells to the cavity.5. At all developmental stages studied, the intracellular potassium concentration is close to 100 m-mole/l. cell water. Intracellular sodium falls steadily from 80 m-mole/l. cell water in eggs to 30 m-mole/l. cell water at the beginning of gastrulation.6. The intracellular sodium activity, measured with sodium sensitive intracellular micro-electrodes, is relatively constant between egg and blastula stages at about 14 mm. During each cell division cycle the intracellular sodium activity rises transiently by 2-3 mM.

SUMMARY1. The sensitivity of the membrane potential of cells of early embryos of Xenopus laevis to variations in the extracellular concentrations of sodium and potassium has been determined.2. Alterations in the extracellular sodium concentration have little effect on the membrane potential at all pregastrular stages tested.3. Up to the 32 cell stage an increase in the concentration of potassium in the bathing medium causes a fall in cell membrane potential only when membrane newly synthesized in the furrow during cleavage is exposed at the embryo surface, during the second half of the cell division cycle.4. Beyond the morula stage (48 cells) a fall in membrane potential on raising external potassium can only be demonstrated when the seal which isolates the intercellular fluid from the bathing medium is broken so that cells lining the inner face of the embryo come into contact with the high potassium solution.5. The results suggest that the egg membrane has little selective permeability whereas membrane synthesized after fertilization is highly potassium permeable.6. No evidence could be obtained for any potential difference between the intercellular fluid and the external bathing medium.7. Dinitrophenol, sodium azide and cyanide prevented normal development only if they were injected into the intercellular cavity. Embryos reared in solutions containing these poisons turned into normal tadpoles.8. The formation of the intercellular cavity could be halted by injecting

Digital flexor tendons isolated from 17-18 day embryonic chickens were cultured intact, either on steel mesh grids, or in an apparatus designed to apply a mechanical load to the tissue. Tendons cultured without an applied load continued to synthesize protein and glycosaminoglycans throughout a 7-day period, but DNA synthesis decreased during this time. Increases in both protein and DNA synthesis were observed in tendons experimentally loaded for 48-72 h. Glycosaminoglycan production by tendons isolated from 17-day embryos was also increased in loaded tendons, sulfated GAG being increased more than hyaluronic acid. The same loading regime applied to tendons from 18-day embryos produced a smaller, yet significant increase in sulfated glycosaminoglycans but hyaluronate production was reduced. These investigations demonstrate that embryonic chicken tendons can be maintained in a viable state in organ culture and may provide a useful model for studies of the effects of mechanical forces on the synthetic capability and structure of connective tissue cells.

No abstract

No abstract