Phosphatide Formation in Tissue Slices

The question whether a tissue can synthesize phosphatides independently or whether it acquires phosphatides from the plasma only after their formation by a more active tissue, was answered by Chaikoff et al. (62) in the following manner. A sciatic nerve of a dog stripped free of all adipose and connective tissue and weighing 300 mg. was placed in 5 ml. of Ringer solution containing radioactive phosphate. For control purposes the adipose-connective tissue surrounding the nerve was treated in a similar way. Conversion of radiophosphate from the Binger solution into radiophosphatide by the nerve was found to be considerable, as is seen in Table XVIII. These experiments show that the nerve process, separated from the nerve cell body, can form phosphatides from inorganic phosphate. 

Time interval, hr. Nerve Adip Me oonneotive tissue 

Similar values were obtained for formation of radioactive phosphatide in brain slices of young and old rats. In the course of 4 hours 0.70 to 0.85% of the labeled phosphorus of Ringer solution was incorporated in brain slices (per gram wet tissue) in brain homogenate lower values (0.20 to 0.22) were obtained, as is seen In Table XIX. 

All values are expressed as per cent of labeled phosphorus of the bath incorporated into phosphatide per gram of tissue. All values recorded for 1, 2, and 4 hours have had the average zero-time value subtracted. 

This type of phosphorylation can only be detected by making use of labeled phosphate. The usual methods of chemical analysis fail to detect the synthesis of the small percentage of new phosphatide molecules, as the formation of these goes hand in hand with the autolysis of a comparatively large percentage of phosphatide molecules present at the start of the experiment. The amount of phosphatide found in brain homogenate after 4 hours is 10-15% less than that present at zero time. 

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