Calcium-induced interaction of phospholipid vesicles and bilayer lipid membranes.

The interaction of unilamellar phospholipid vesicles with bilayer lipid membranes has been studied by observing the electrical conductance of the planar membrane. The presence of phosphatidylcholine vesicles as well as phosphatidylcholine/phosphatidylserine (1 : 1) vesicles on one side compartment of the bilayer membrane, but not phosphatidylserine vesicles, causes discrete fluctuations in the phosphatidylserine membrane conductance, which is also increased by at least an order of magnitude. These events are dependent on vesicle concentration as well as the presence of Ca2+. The results are interpreted in terms of the incorporation of domains of phosphatidylcholine into the membrane, which confer a higher conductance state.