Studies on the composition of phospholipids in rat small intestinal smooth muscle

The phospholipid composition of rat small intestinal smooth muscle was investigated in comparison with those of the mucosa and liver. Phospholipid content per g of the wet smooth muscle was almost identical with that of the mucosa and was about 1/4 of that in the liver. The phospholipid/protein ratio of the smooth muscle was about 1/2 of the value in the liver. Sphingomyelin content was significantly high and amounted to 18% of total phospholipids. This value was about twice that in the mucosa and 4 times higher than that in the liver. On the other hand, the percent distribution of phosphatidylcholine was lowest in the smooth muscle. Distribution patterns of phosphatidylserine and phosphatidylinositol in the smooth muscle as well as in the mucosa were different from those in the liver. The occurrence of vinyl-ether and ether phospholipids was clearly demonstrated in the smooth muscle as well as in the mucosa. A major part of the ether lipids was detected in the phosphatidylethanolamine fraction, in which they amounted to about 50%; 40% as alkenyl-acyl type and 12% as alkyl-acyl type. A high content of ether lipids was also observed in the phosphatidylethanolamine fraction from mucosa, but the distribution was reversed, that is, 14% alkenyl-acyl type and 28% alkyl-acyl type. Fatty aldehydes, fatty alcohols, and fatty acids were also determined by gas-liquid chromatography. The compositions of fatty aldehydes in the phosphatidylethanolamine fraction from smooth muscle and from mucosa were similar, whereas the compositions of long chain fatty alcohol and fatty acids were clearly different. The compositions of fatty alcohols and fatty acids of the phosphatidylcholine fraction from smooth muscle showed significantly different patterns from those of the phosphatidylethanolamine fraction and from those of the same phospholipid fraction in the mucosa.