The phosphatidylcholine content of both the intestinal and renal brush-border membranes and ion transport are affected by 1,25-dihydroxycholecalciferol (1,25(OH)2D3). To investigate the mechanism of this effect, liposomes were prepared containing self-quenching concentrations of fluorescent phospholipid derivatives. When these liposomes were incubated with rat renal brush-border membrane vesicles, an immediate increase in the relative fluorescence of N-4-nitrobenz-2-oxa-1,3-diazole phosphatidylcholine (NBD-PC) was detected, indicating transfer of NBD-PC into a non-quenched membrane. Addition of 1,25(OH)2D3 to the liposomes produced a dose-dependent stimulation of NBD-PC transfer to the acceptor brush-border membrane vesicles. Peripheral fluorescence was visible when the brush-border membrane vesicles were viewed with a fluorescent microscope. Using brush-border membrane vesicles from kidneys of vitamin D-deficient animals, quantitation of lipid transfer revealed a 1,25(OH)2D3 (10-7 M) stimulation of NBD-PC transfer from 1.38 ± 0.27 to 2.07 ± 0.26 μg/h, and of PC transfer, assessed by vesicle phosphatidylcholine content, from 49.7 ± 12 to 57.3 ± 12 μg/mg protein per h (P < 0.05). There was no significant transfer of N-(lissamine rhodamine B sulfonyl)dioleoylphosphatidylethanolamine (N-Rh-PE). In the absence of hormone, the amount of NBD-PC transferred to brush-border membrane vesicles prepared from normal rats was significantly greater than that transferred to brush-border membrane vesicles prepared from vitamin D-deficient animals (2.12 ± 0.02 vs. 1.39 ± 0.27 μg of NBD-PC/h, P < 0.05). Both physiologic and pharmacologic concentrations of 1,25(OH)2D3 stimulated NBD-PC transfer with maximum response at 10-14 M (2.98 ± 0.15 μg/h). 24,25-Dihydroxycholecalciferol and 25-hydroxycholecalciferol (25(OH)D3) also stimulated transfer, although dose-response curves were less effective than for 1,25(OH)2D3. Cortisol and vitamin D-3 did not stimulate transfer. 1,25(OH)2D3 did not stimulate NBD-PC transfer between liposome populations.
- (Rat kidney brush-border membrane)
- N-4-Nitrobenz-2-oxa-1,3-diazole phosphatidylcholine
- Phospholipid transfer
- Vitamin D