Combined effects of magnesium deficiency and an atherogenic level of low density lipoprotein on uptake and metabolism of low density lipoprotein by cultured human endothelial cells. II. Electron microscopic data.

The effects of magnesium deficiency on low density lipoprotein (LDL) transport by cultured endothelial cells with a high concentration of LDL (2 mg of LDL cholesterol/ml) were investigated by electron microscopy and by counting the radioactivity of [3H]-LDL transported across an endothelial monolayer grown on culture plate inserts. Electron microscopic examination showed that the number of pits/vesicles in the apical side was time-dependently increased for 24 h in both magnesium-deficient and magnesium-sufficient groups with the exception of 1 h under magnesium sufficiency. The number of pits/vesicles in the basal side was also increased for 8 h in both groups, though there was a decrease at 24 h in the two groups. No difference between either magnesium group at the same time point was statistically significant. [3H]-LDL transport was also time-dependently increased in both magnesium-deficient and magnesium-sufficient groups. In contrast to the results obtained by electron microscopy, the amount of LDL transported under magnesium deficiency was much larger for 24 h than under magnesium sufficiency. Differences in LDL transport between magnesium groups were statistically significant at 4 and 8 h. This finding indicates that magnesium deficiency increases LDL transport across the endothelial monolayer. The increase may be due to energy-dependent movement across endothelial cells, energy-independent movement between cells, or both. However, we conclude that magnesium deficiency increases the energy-dependent LDL transport to some degree since intercellular gap formations were rarely observed in either magnesium group. This LDL transported to the subendothelial space may lead to LDL accumulation and initiate atherosclerosis.