Membrane perturbation by mastoparan 7 elicits a broad alteration in lipid composition of L1210 cells

Mastoparan 7 (Mas-7), an amphiphilic peptide possessing membrane perturbing activity, has been known to selectively stimulate some lipases. To examine changes in the lipid composition induced by Mas-7, we carried out systemic lipid analysis of L1210 cells after Mas-7 treatment. The total lipid was determined by HPLC, gas-liquid chromatography, and electrospray ionization mass spectrometry in conjunction with differential radiolabelling with [32P]orthophosphate, [3H]myristic acid, and [3H]arachidonic acid. The lipid analysis revealed multiple changes in more than 10 lipid classes. Free fatty acids (FFAs) and phosphatidylethanol (PEt), the phospholipase D product in the presence of ethanol, were increased significantly and phosphatidylcholine (PC) was decreased. Digitonin, a membrane permeabilizing reagent, similarly affected the lipid composition of L1210. The FFA released showed a very broad distribution of saturated, monounsaturated, and polyunsaturated fatty acids, implying that phospholipase A2 alone could not account for all of the FFAs released. By comparing the molecular species of PEt with those of endogenous PC, we showed that phospholipase D in L1210 cells appeared to act selectively on diacyl-PC. The perturbation-induced alterations in the lipid composition brought about by Mas-7 might play a crucial role in the physiology of the affected cells.