The Role of Membrane Lateral Tension in Calcium-Induced Membrane Fusion

The Role of Membrane Lateral Tension in Calcium-Induced Membrane Fusion Calcium-induced fusion of liposomes was studied with a view to understand the role of membrane tension in this process. Lipid mixing due to fusion was monitored by following fluorescence of rhodamine-phosphatidyl-ethanolamine incorporated into liposomal membrane at a self-quenching concentration. The extent of lipid mixing was found to depend on the rate of calcium addition: at slow rates it was significantly lower than when calcium was injected instantly. The vesicle inner volume was then made accessible to external calcium by adding calcium ionophore A23187. No effect on fusion was observed at high rates of calcium addition while at slow rates lipid mixing was eliminated. Fusion of labeled vesicles with a planar phospholipid membrane (BLM) was studied using fluorescence microscopy. Above a threshold concentration specific for each ion, Ca2+, Mg2+, Cd2+ and La3+ induce fusion of both charged and neutral membranes. The threshold calcium concentration required for fusion was found to be dependent on the vesicle charge, but not on the BLM charge. Pretreatment of vesicles with ionophore and calcium inhibited vesicle fusion with BLM. This effect was reversible: chelation of calcium prior to the application of vesicle to BLM completely restored their ability to fuse. These results support the hypothesis that tension in the outer monolayer of lipid vesicle is a primary reason for membrane destabilization promoting membrane fusion. How this may be a common mechanism for both purely lipidic and protein-mediated membrane fusion is discussed. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

The Role of Membrane Lateral Tension in Calcium-Induced Membrane Fusion

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Publisher
Springer-Verlag
Copyright
Copyright © Inc. by 2000 Springer-Verlag New York
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232001076
Publisher site
See Article on Publisher Site

Abstract

Calcium-induced fusion of liposomes was studied with a view to understand the role of membrane tension in this process. Lipid mixing due to fusion was monitored by following fluorescence of rhodamine-phosphatidyl-ethanolamine incorporated into liposomal membrane at a self-quenching concentration. The extent of lipid mixing was found to depend on the rate of calcium addition: at slow rates it was significantly lower than when calcium was injected instantly. The vesicle inner volume was then made accessible to external calcium by adding calcium ionophore A23187. No effect on fusion was observed at high rates of calcium addition while at slow rates lipid mixing was eliminated. Fusion of labeled vesicles with a planar phospholipid membrane (BLM) was studied using fluorescence microscopy. Above a threshold concentration specific for each ion, Ca2+, Mg2+, Cd2+ and La3+ induce fusion of both charged and neutral membranes. The threshold calcium concentration required for fusion was found to be dependent on the vesicle charge, but not on the BLM charge. Pretreatment of vesicles with ionophore and calcium inhibited vesicle fusion with BLM. This effect was reversible: chelation of calcium prior to the application of vesicle to BLM completely restored their ability to fuse. These results support the hypothesis that tension in the outer monolayer of lipid vesicle is a primary reason for membrane destabilization promoting membrane fusion. How this may be a common mechanism for both purely lipidic and protein-mediated membrane fusion is discussed.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Jul 1, 2000

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