N-Acylphosphatidylethanolamine Accumulation in Potato Cells upon Energy Shortage Caused by Anoxia or Respiratory Inhibitors

A minor phospholipid was isolated from potato (Solanum tuberosum L. cv Bintje) cells, chromatographically purified, and identified by electrospray ionization mass spectrometry as N-acylphosphatidylethanolamine (NAPE). The NAPE level was low in unstressed cells (13 ± 4 nmol g fresh weight(−1)). According to acyl chain length, only 16/18/18 species (group II) and 18/18/18 species (group III) were present. NAPE increased up to 13-fold in anoxia-stressed cells, but only when free fatty acids (FFAs) started being released, after about 10 h of treatment. The level of groups II and III was increased by unspecific N-acylation of phosphatidylethanolamine, and new 16/16/18 species (group I) appeared via N-palmitoylation. NAPE also accumulated in aerated cells treated with NaN(3) plus salicylhydroxamate. N-acyl patterns of NAPE were dominated by 18:1, 18:2, and 16:0, but never reflected the FFA composition. Moreover, they did not change greatly after the treatments, in contrast with O-acyl patterns. Anoxia-induced NAPE accumulation is rooted in the metabolic homeostasis failure due to energy deprivation, but not in the absence of O(2), and is part of an oncotic death process. The acyl composition of basal and stress-induced NAPE suggests the existence of spatially distinct FFA and phosphatidylethanolamine pools. It reflects the specificity of NAPE synthase, the acyl composition, localization and availability of substrates, which are intrinsic cell properties, but has no predictive value as to the type of stress imposed. Whether NAPE has a physiological role depends on the cell being still alive and its compartmentation maintained during the stress period

The use of fluorescamine as a permeant probe to localize phosphatidylethanolamine in intact friend erythroleukaemic cells

Intact Friend erythroleukaemic cells (Friend cells) were incubated at 0–4°C with increasing amounts of fluorescamine. Phospholipids were extracted and the amounts of phosphatidylethanolamine and of its fluorescamine derivative were determined. (1). The plasma membrane of intact Friend cells appeared to be permeable to fluorescamine in a concentration-dependent way. (2). Three pools of phosphatidylethanolamine could be detected as the fluorescamine concentration was raised. The two first pools were ascribed to the outer monolayer (16–17% of the total cellular phosphatidylethanolamine) and inner (17–18%) monolayer of the plasma membrane, respectively, indicating an essentially symmetrical distribution of this phospholipid. The third pool of phosphatidylethanolamine (66%) corresponds to the contribution of intracellular membranes. (3). These data were used in turn, to calculate the relative amount of each phospholipid class present in the plasma membrane. The results are in perfect agreement with those obtained by an independent method involving the use of sphingomyelinase C (Rawyler, A., Roelofsen, B., Op den Kamp, J.A.F. and Van Deenen, L.L.M. (1983) Biochim. Biophys. Acta 730, 130–138). The present method is discussed in terms of its applicability for the localization of phosphatidylethanolamine in eukaryotic cells