Two separate pools of sphingomyelin in BHK cells.
In BHK cells labelled to equilibrium with [3H]choline and treated with sphingomyelinase the surface pool of sphingomyelin is degraded very rapidly (half-time 10 min) but the internal pool of sphingomyelin which accounts for about 30% of the total is only degraded slowly (half-time about 80 h) showing that the internal pool does not normally reach the surface. In [3H]choline incorporation experiments the internal pool begins to accumulate radioactivity at about the same time as phosphatidylcholine (30 min) but label does not enter the surface pool of sphingomyelin for a further 90 min. The internal and external pools reach the same specific activity only after about 20 h. Pulse-chase analysis with [3H]choline shows that radioactivity in each pool of sphingomyelin continues to increase when the specific radioactivity of phosphatidylcholine is decreasing, consistent with both pools being synthesised from a phosphatidylcholine precursor. The results suggest that sphingomyelin in BHK cells is present not only in the plasma membrane but also in a more rapidly labelling pool which does not mix with the surface pool.
Quinn
P
P
Department of Physiology, University College London, U.K.
Allan
D
D
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002794:Choline / Q000378:metabolism; D007700:Kinetics; D013109:Sphingomyelins / Q000378:metabolism*
D013109:Sphingomyelins; D002794:Choline