Membrane Lipid Alterations and Na⁺-Pumping Activity in Erythrocytes From IDDM and NIDDM Subjects

The Na⁺-pumping activity of the erythrocyte plasma membrane in diabetic subjects was studied together with the lipid composition. Insulin-dependent diabetes mellitus (IDDM) patients (n = 25) were divided into young (28.1 ± 7.4 yr old, mean ± SD; n = 16) and old (71.7 ± 9.8 yr old; n = 10) subjects; the age of non-insulin-dependent (NIDDM) patients was 70.7 ± 11.5 yr (n = 10). The Na⁺-pumping activity, estimated from both Na⁺-K⁺-ATPase and ouabain binding, was significantly decreased in IDDM and NIDDM subjects, but its insulin sensitivity was retained only in young IDDM subjects. The total cholesterol and phospholipid content of the erythrocyte plasma membrane was lowered in IDDM subjects, and cholesterol-to-phospholipid molar ratio was significantly decreased. In NIDDM subjects the significant decrease of the two lipid components did not alter their ratio. The analysis of major phospholipid components of erythrocyte membranes revealed that only phosphatidylcholine is significantly increased in young diabetic subjects. The fatty acid composition of major phospholipid classes was significantly altered in all cases: the unsaturation index appeared to be increased in phosphatidylserine and sphingomyelin for both IDDM and NIDDM subjects and was also increased in phosphatidylcholine in the latter group.