Relationship between Erythrocyte Membrane Phase Properties and Susceptibility to Secretory Phospholipase A₂

Abstract

Normally, cell membranes resist hydrolysis by secretory phospholipase A 2 . However, upon elevation of intracellular calcium, the cells become susceptible. Previous investigations demonstrated a possible relationship between changes in lipid order caused by increased calcium and susceptibility to phospholipase A 2 . To further explore this relationship, we used temperature as an experimental means of manipulating membrane physical properties. We then compared the response of human erythrocytes to calcium ionophore at various temperatures in the range of 20-50 °C using fluorescence spectroscopy and two-photon fluorescence microscopy. The steady state fluorescence emission of the environmentsensitive probe, laurdan, revealed that erythrocyte membrane order decreases systematically with temperature throughout this range, especially between 28 and 45 °C. Furthermore, the ability of calcium ionophore to induce increased membrane order and susceptibility to phospholipase A 2 depended similarly on temperature. Both responses to calcium influx were enhanced as membrane fluidity increased. Analysis of the spatial distribution of laurdan fluorescence at several temperatures indicated that the ordering effect of intracellular calcium on fluid membranes generates an increase in the number of fluid-solid boundaries. Hydrolysis of the membrane appeared to progress outward from these boundaries. We conclude that phospholipase A 2 prefers to hydrolyze lipids in fluid regions of human erythrocyte membranes, but primarily when those regions coexist with domains of ordered lipids.

Investigation into the role of phosphatidylserine in modifying the susceptibility of human lymphocytes to secretory phospholipase A2 using cells deficient in the expression of scramblase

“…5 and 7 have been suggested to be essential for cells to become susceptible to sPLA 2 [7,8,39,40]. The data shown here would argue the same since the cells hydrolyzed at the highest rate (S49) also displayed the largest alteration in MC540 and TMA-DPH fluorescence upon addition of ionomycin.…”

Secretory phospholipase A2 type III enhances α-secretase-dependent amyloid precursor protein processing through alterations in membrane fluidity

“…sPLA 2 -III from bee venom is highly homologous to the enzymatic-active central s-domain of human sPLA . This protein has been reported to alter cellular membrane properties ( 29 ). In this study, we investigate whether sPLA 2 -III alters sAPP ␣ in differentiated neuronal cells, including SH-SY5Y cells and primary rat neurons, and A ␤ secretion.…”

The effect of experimental hyperoxia on erythrocytes’ oxygen-transport function

“…It is known that medium pH can affect the shape and deformability of erythrocytes [59,60], membrane proteins and the phospholipid bilayer [61][62][63][64] and the stability of the cytoskeleton [65][66][67]. In addition, pH changes can affect the transmembrane transport of substances, reducing the rate of diffusion of oxygen in the lipid bilayer.…”