1981 Volume 89 Issue 2 Pages 665-675
When chicken erythrocytes labeled with a stearic acid derivative spin label were treated with concanavalin A (Con A), ESR spectra showed a change in the peaks due to the labels in membrane lipids, indicating an increase of membrane lipid fluidity. Addition of Con A increased the fluidity rapidly. This change was reversible only up to 30min after adding Con A, and thereafter it gradually became irreversible. However, if the erythrocytes were treated with cytochalasin B and methyl α-D-man-noside, a complete return of fluidity to the normal level could be observed at any stage after the binding of Con A. The observation of freeze-fracture replicas of erythrocyte membranes by transmission electron microscopy also showed that the redistribution of intramembranous particles gradually became irreversible after exposure to Con A. These results suggest that the microfilament-like system, which modulates the distribution of cell surface receptors for Con A, participates in the modulation of membrane fluidity.
Phospholipid methylation of chicken erythrocyte membrane was stimulated immediately after the binding of Con A. A methyltransferase inhibitor, 5'-deoxy-5'-S-isobutyl adenosine, abolished the increase of membrane fluidity within the first 10min and also that occurring later than 60min after adding Con A, but it was without effect on the elevated fluidity found between 20 and 60min. Removal of extracellular Ca2+ had an inhibitory effect on the lasting increase of fluidity. These results suggest that the first increase of membrane fluidity by Con A may be caused by phospholipid methylation, while the second increase may depend on the rearrangement of Con A receptor glycoproteins through cross-linking with Con A. The irreversible part of the membrane fluidity increase probably depends on Ca2+ influx, phospholipid methylation, and peripheral membrane proteins which constitute the microfilament-like system at the membrane inner surface.
