Effect of 27-hydroxycholesterol on cellular sphingomyelin synthesis and Ca++ content in cultured smooth muscle cells.

The relationships among sphingomyelin synthesis cytosolic free Ca++ level and cytotoxicity in the presence of 27-hydroxycholesterol were investigated by measurement of [methyl-3H] choline incorporation into sphingomyelin, phosphatidylcholine, phosphocholine and cytidine choline 5'-diphosphate, 45Ca++ uptake, cytosolic free Ca++ levels and viable cell numbers. The results indicated that 27-hydroxycholesterol at higher than normal level induced increased [3H] choline incorporation in sphingomyelin accompanied by decreased radioactivity in phosphatidylcholine but did not alter [3H] choline content in phosphocholine and cytidine choline 5'-diphosphate. The increased radioactivity in sphingomyelin by 27-hydroxycholesterol was detected first, followed by detection of the enhanced Ca++ uptake and cytosolic free Ca++. Finally, a decrease in viable cell number occurred. We suggest that the increased transfer from phosphatidylcholine to sphingomyelin by 27-hydroxycholesterol may be related to enhanced cytosolic free Ca++.