Kinetics of cholesterol movement between liposomes and intestinal brush border membrane vesicles
Sanyal, S.N.; Sadana, T.; Majumdar, S.
Indian Journal of Experimental Biology 25(10): 674-680
1987
ISSN/ISBN: 0019-5189 PMID: 3450589 Document Number: 296735
Spontaneous (14C)-cholesterol movement occurs between egg yolk PC-cholesterol lipid vesicles and vesicles prepared from rhesus monkey small intestinal brush border membrane vesicles (BBMV) in physiological buffer at 37.degree. C[Can J Biochem Cell Bio, 64 (1986) 575]. Further study of the reaction showed the following features: (1) The rate of cholesterol transfer from sonicated unilamellar vesicles (ULV) to BBMV followed apparently first order kinetics. Intermembrane cholesterol movement was strikingly similar in both the directions. However, from BBMV to ULV, the transfer rate was three times faster than that of ULV to BBMV. (2) Similarity in the rate constant was observed when cholesterol transfer was studied using either large multilamellar lipid vesicles (MLV) or ULV as donor and BBMV as the acceptor particle. Rate constant was also the same when the acceptor membrane used was either intact BBM vesicles of ULV prepared from BBM lipids. (3) The rate of transfer of label was not affected even when the acceptor vesicle concentration was increased linearly over 5-folds, indicating the first order nature of the reaction. (4) Transfer of cholesterol from ULV to BBMV was accelerated by the presence of acetone, dimethyl sulfoxides (DMSO), deoxycholate and papain over several folds. Partially purified rat liver cytosolic non-specific lipid exchange protein increased the rate of cholesterol transfer by about 4-folds. (5) Reduction in BBM cholesterol and phospholipid content was noted by DMSO, acetone and deoxycholate while papain caused a small amount of depletion of membrane proteins. (6) Cholesterol transfer is temperature dependent with an activation energy of 31K Joule, mole-1, which is almost identical in the presence or absence of non-specific lipid exchange protein. The molecular mechanism of intermembrane cholesterol movement is discussed in view of the kinetic and thermodynamic data obtained. (7) BBM vesicles were found stable and suitable for use in cholesterol transfer experiments upon long term incubations by retaining most of the radiolabelled cholesterol incorporated in their membrane lipid bilayer and also by near complete recovery of the BBM-associated marker enzyme activities. Purity of the membrane preparation was established in that, the isolated BBM showed 13- to 17-folds enrichment in terms of the marker enzyme activities when compared to the initial intestinal homogenates with more than 80% recovery. (8) Intestines from hypertensive rhesus monkeys were also included in the study which however did not show any difference from the normal ones in respect to any of the above mentioned parameters tested.