Phospholipid exchange between plasma and erythrocytes in man and the dog

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Abstract
The turnover of the four major erythrocyte phospholipids has been studied with 32P, both in vivo and in vitro, in man and the dog. Phosphatidyl serine and phosphatidyl ethanolamine appeared to be stable erythrocyte lipids in both species. Turnover of the phosphate moiety of lecithin and sphingomyelin in the circulating erythrocytes of these two species seems entirely due to an exchange of the whole molecule with the corresponding plasma compound. Exchangeable and nonexchangeable pools of these two cellular lipids were found. In man about 60% of erythrocyte lecithin is exchangeable. The 12 hr fractional turnover of this pool is approximately 13%. Only 30% of the sphingomyelin in human cells appeared exchangeable; this portion had a 12 hr fractional turnover of about 14%. Similar results were obtained in the dog except that in this species about 75% of the erythrocyte sphingomyelin was exchangeable. Inorganic 32P was not incorporated into any of the four major phospholipids in either species. The present findings aid in estimating quantitatively the effect of plasmaerythrocyte lipid exchange on red blood cell phospholipids.