Veratridine-induced depolarization reduces the palmitoylation of brain and myelin glycerolipids.

In this study, we have investigated the effect of neuronal depolarization on the palmitoylation of myelin lipids. For this purpose, brain slices from 60-day-old rats were incubated with [3H]palmitate for 1 h in the presence or absence of various drugs. Veratridine (100 microM) reduced the incorporation of [3H]palmitate into all brain glycerolipids by 40-50%, whereas the labeling of sphingolipids was unaffected. Similar results were obtained by using [3H]glycerol as a precursor, demonstrating that veratridine also causes a reduction in the de novo synthesis of glycerolipids. Both tetrodotoxin (1 microM) and ouabain (1 mM) prevented the effect of veratridine, indicating that it is mediated through the opening of voltage-gated sodium channels and involves the stimulation of the Na+/ K+ pump. Decreased levels of both ATP, due to activation of the Na+,K+-ATPase, and the precursor palmitoyl-CoA were found in the veratridine-treated slices, thus explaining the reduction in lipid synthesis. Neuronal depolarization also decreased the synthesis of lipids present in the myelin fraction. The relatively high specific radioactivity of myelin lipids and the results from both repeated purification experiments and mixing experiments ruled out the possibility that the radioactive lipids present in myelin could derive from contamination with other subcellular fraction(s). Because neither mature oligodendrocytes nor myelin is known to express voltage-dependent Na+ channels, it is conceivable that the effect of veratridine on myelin glycerolipid metabolism occurs by an indirect mechanism such as an increase in the extracellular [K+]. However, the presence of 60 mM KCl in the medium did not affect the acylation of either brain or myelin lipids. These results raise questions as to the absence of sodium channels in myelinating oligodendrocytes and/or myelin.