Replacement of mouse LM fibroblast choline by a sulfonium analog. Effects on membrane properties as determined by virus probes

A sulfonium analog of choline ('sulfocholine', a natural phospholipid constituent of diatoms) was metabolically incorporated into mouse LM fibroblasts cultured in serum-free medium. Subconfluent cultures of LM cells were able to utilize sulfocholine as sole choline source and to increase in cell number for 3 days of incubation; thereafter a decrease in cell number was observed. In contrast, cultures of LM cells seeded to confluency showed no decrease in cell number up to at least 10 days when maintained, with daily medium changes, in medium containing either choline or the sulfonium analog. Such confluent cultures, maintained for 7 days in sulfocholine-containing medium, showed virtually complete replacement of cellular phosphatidylcholine and greater than 50% replacement of cellular sphingomyelin by their respective sulfonium analogs. The functional exchangeability of natural phosphatidylcholine and sphingomyelin with their sulfonium analogs to participate in normal cell membrane-mediated activities was demonstrated by comparatively assaying the abilities of sulfocholine- and choline-maintained cells to incorporate and replicate certain animal viruses known to possess membrane-dependent steps in various phases of their replication cycles. No difference was detected between the abilities of sulfocholine- and choline-maintained cells to take up vesicular stomatitis virus or mengo virus, or to replicate vesicular stomatitis virus, mengo virus or mouse hepatitis virus.