Preparation and some properties of giant liposomes and proteoliposomes

Optimal conditions for formation of giant liposomes and proteoliposomes were investigated. A suspension of small unilamellar vesicles made of various phospholipids in a buffer of 0-3 M KCl, 0.1 mM EDTA, and 20 mM MOPS (pH 7.0) was subjected to a freeze-thaw treatment. Giant multilamellar liposomes of diameter ranging from 10 to 60 microns were found to form from phospholipid mixtures containing phosphatidylethanolamine as a major component and phosphatidylserine as a minor component. The concentration of KCl optimal for the giant vesicle formation was 30-500 mM. By applying a patch-pipette to a giant liposome, suitable conditions for obtaining a high-resistance (giga-ohm) seal were sought. It was found that use of a patch-pipette of relatively small tip diameter (less than 1 micron), the presence of divalent metal cations in the suspension medium and inflation of vesicles in a hypotonic solution facilitated giga-seal formation. In a suspension of asolectin (soybean phospholipid) vesicles which had been subjected to the freeze-thaw treatment, giant unilamellar vesicles were found. They could be held on the tip of a suction pipette and impaled with a microelectrode filled with an EGTA solution. Small unilamellar proteoliposomes were prepared by the cholate-dialysis method from asolectin and sarcoplasmic reticulum vesicles, and were subjected to a freeze-thaw cycle. When the ratio of exogenous phospholipid to protein was larger than 10, giant multilamellar vesicles were formed.(ABSTRACT TRUNCATED AT 250 WORDS)