Skeletal muscle phosphatidylcholine fatty acids and insulin sensitivity in normal humans

The fatty acid composition of skeletal muscle membrane phospholipids (PL) is known to influence insulin responsiveness in humans. However, the contribution of the major PL of the outer (phosphatidylcholine, PC) and inner (phosphatidylethanolamine, PE) layers of the sarcolemma to insulin sensitivity is not known. Fatty acid composition of PC and PE from biopsies of vastus lateralis from 27 normal men and women were correlated with insulin sensitivity determined by the hyperinsulinemic euglycemic clamp technique at insulin infusion rates of 0.4, 1.0, and 10.0 mU. kg^-1. min^-1. Significant variation in the half-maximal insulin concentration (ED₅₀) was observed in the normal volunteers (range 24.0-146.0 μU/ml), which correlated directly with fasting plasma insulin (r = 0.75, P < 0.0001). ED₅₀ was inversely correlated with the degree of membrane unsaturation (C₂₀C₂₂ polyunsaturated fatty acids; r = 0.58, P < 0.01) and directly correlated with fatty acid elongation (ratio of 16:0 to 18:0, r = 0.45, P < 0.05) in PC. However, no relationship between fatty acid composition and insulin sensitivity was observed in PE (NS). These studies suggest that the fatty acid composition of PC may be of particular importance in the relationship between fatty acids and insulin sensitivity in normal humans.