F. Bellemare et al., CHARACTERISTICS OF EXOGENOUS LIPID UPTAKE BY RENAL AND INTESTINAL BRUSH-BORDER MEMBRANE-VESICLES, Biochemistry and cell biology, 73(3-4), 1995, pp. 171-179
The transfer of radioactive phosphatidylcholine (PC) from liposomes t
o rabbit jejunal and renal brush-border membrane vesicles (BBMVs) was
measured with a fast-sampling, rapid-filtration apparatus. PC uptake
by jejunal and renal BBMVs was favoured when liposomes were made from
soybean phosphatidylcholine (azolectin, AZO), whereas PC uptake could
not be quantitatively assessed from egg yolk phosphatidylcholine (PC)
liposomes even after a 22-h period of incubation. The increased turbi
dity of BBMV dispersion following the addition of CaCl2 or HCl to AZO-
treated BBMVs suggested that negatively charged lipids and phosphatidy
lethanolamine are transferred during the process. These data and the a
nalysis of PC-uptake time measurements, using an algorithm simulating
aggregation phenomena, indicated that the reaction mechanism involved
liposome aggregation to BBMVs rather than specific lipid transfer. Th
e constants of the dimerization reaction between AZO liposomes and BBM
Vs were evaluated to be 0.016 +/- 0.006 min(-1) for jejunal and 0.095
+/- 0.02 min(-1) for renal preparations. IntravesICULAR D-ASPartic aci
d accumulation in the presence of a Na+ gradient indicated that vesicl
es were still closed after coincubation with liposomes. In contrast, 7
0-85% of rabbit jejunal and renal Na+-D-glucose cotransporter activiti
es were lost after overnight incubation with either AZO liposomes or b
uffered solution. Further, H+-ATPase activity in rabbit renal BBMVs la
rgely decreased after coincubation with AZO liposomes, while brush-bor
der membrane associated enzymes remained stable. These results demonst
rate that coincubation of BBMV with liposomes of different composition
may represent a useful approach to study the influence of lipidic env
ironment on various membrane protein functions.