Axon-myelin transfer of glycerol-labeled lipids and inorganic phosphate during axonal transport.
Axon-to-myelin transfer of lipids precursors have been studied in the rabbit optic system by intraocular injection of [32P]orthophosphate, [14C]glycerol and [3H]glycerol. Choline and ethanolamine phosphoglycerides and myelin showed increasing [32P]-radioactivity between 7 and 21 days following injection, while [3H]- and [14C]-radioactivities remained relative constant. The latter radioactivities decreased, however, in all the axon- and axolemma-enriched fractions during the same period. These findings supported the concept that a portion of substances undergoing axonal transport enters the pool of myelin lipids by two mechanisms: transcellular transfer of intact lipid and axon-myelin transfer of precursors which are re-utilized for lipid biosynthesis by myelin-localized enzymes. The present study shows that inorganic phosphate, possibly generated by catabolic activity within the axon, is able to enter myelin and participate in the re-utilization mechanism as previously described for serine, choline and acyl chains. The relative invariance of the 3H:14C ratio suggested that the majority of glycerol is not re-utilized in this manner but probably enters myelin through transfer of intact lipid. These and earlier results suggest a possible form of metabolic dependence of myelin on tropine substances from the axon.
D000818:Animals; D001370:Axonal Transport; D001369:Axons / Q000378:metabolism*; D005829:Geniculate Bodies / Q000378:metabolism; D050356:Lipid Metabolism; D009186:Myelin Sheath / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000378:metabolism; D011817:Rabbits; D013477:Superior Colliculi / Q000378:metabolism; D014795:Visual Pathways / Q000378:metabolism*
D010710:Phosphates; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines