Biomedical subjects

J P Lovejoy

Publications and source records attributed to J P Lovejoy.

4 recordsLinked to original sources

PubMed1984

Lateral phase separation of phospholipids as a basis for increased permeability of membranes towards fluorescein and other chemical species.

Using mouse spleen cells, before and after treatment with glutaraldehyde or mild hyperthermia, we observe a strong correlation between permeability to fluorescein and susceptibility to staining with N epsilon-dansyl-L-lysine (irrespective of the cells' ability to exclude trypan blue). We observe the same correlation using liposomes prepared from phosphatidylcholine and varying amounts of cholesterol. We have recently introduced N epsilon-dansyl-L-lysine as a fluorescent membrane stain, or "probe," whose uptake, we propose, is selective for phospholipid domains in membranes (G.M.K. Humphries & J.P. Lovejoy Biophys. J. 42:307-310, 1983; G.M.K. Humphries & J.P. Lovejoy J. Membrane Biol. 77:115-122, 1984). The results presented here are consistent with the hypothesis that the presence or absence of phospholipid domains in membranes also modifies their permeability toward fluorescein, and suggests that permeability towards other chemical species may be similarly affected. On the basis of work using liposomes, we believe this to be the case for carboxyfluorescein and for glucose.

Animals↗

PubMed1984

Membrane structure and the tenuously maintained resistance to staining with N epsilon-dansyl-L-lysine shown by many cells.

The ability to resist staining by N epsilon-dansyl-L-lysine is tenuously maintained in the majority of live nucleated cells taken from tissues concerned with immune function. Resistance is lost under a variety of nonphysiological conditions known to, or likely to, cause protein denaturation or aggregation. In contrast to that of dansyl-gamma-aminobutyrate, the fluorescence intensity of N epsilon-dansyl-L-lysine is only weakly enhanced by native proteins. This is further reduced on denaturation or aggregation of the proteins. It is unlikely, therefore, that cellular uptake of, and staining by, N epsilon-dansyl-L-lysine is a direct consequence of membrane protein denaturation/aggregation but may result from a decrease in protein-phospholipid interactions leading to formation of phospholipid domains. Previous work has indicated that such features are stained by N epsilon-dansyl-L-lysine (Humphries, G.M.K., Lovejoy, J.P., 1983, Biophys. J. 42:307-310; Humphries, G.M.K., Lovejoy, J.R., 1983, Biochem. Biophys. Res. Commun. 111:768-774). Although it appears likely that passage through a dansyl-lysine-staining state is a common, if not universal, prelude to cell death (as monitored by uptake of trypan blue), not all cells that lose resistance to dansyl-lysine staining are moribund. Resistance to staining is also lost by macrophages on binding to solid substrates and multivalent ligands. The possible physiological significance of this is discussed.

Animals↗

PubMed1983

Cholesterol-free phospholipid domains may be the membrane feature selected by N epsilon-dansyl-L-lysine and merocyanine 540.

We have used N epsilon-dansyl-L-lysine as a fluorescent membrane probe, to study cells taken from tissues concerned with immune function. There is a striking similarity between the staining selectivity of this compound and that reported by others for merocyanine 540. Both compounds stain leukemic, human, peripheral leukocytes, an erythroleukemia line, and some mouse bone marrow cells, suggesting common selectivity for a membrane feature of hemopoietic cells. Both compounds fail to stain red blood cells, normal human leukocytes, mouse spleen and thymus cells. We have recently reported that dansyl-lysine apparently selects for cholesterol-free phospholipid domains in liposomes and now report similar selectivity for merocyanine 540 staining of liposomes.

Animals↗

PubMed1983

Dansyl lysine: a structure-selective fluorescent membrane stain?

Dansyl lysine (DL) is a fluorescent compound that has significantly higher solubility in synthetic phosphatidylcholine (PC) membranes with a low cholesterol content than it does in water or in membranes having a high cholesterol content. Its fluorescence intensity is enhanced at least 50-fold when dissolved in PC membranes. Therefore, membranes with mole fractions of cholesterol (Xch) less than or equal to 0.5-0.3 are stained by aqueous solutions of DL: those with a higher cholesterol content, 0.3-0.4 less than or equal to Xch less than or equal to 0.5, are not. It is proposed that DL selects for a structural feature of membranes: cholesterol-free domains. The phenomenon has provided evidence for long-lived compositional heterogeneity in large multilamellar PC-cholesterol liposomes having Xch less than or equal to 0.2. This is not consistent with a model in which the homogeneous state is thermodynamically favored and both intermembrane transfer and transmembrane transfer (flip-flop) of cholesterol are fast. These studies are of potential importance for understanding cell membrane structure, in particular lipid-phase equilibria and the maintenance of compositional heterogeneity between the different membranes of cells.

Cholesterol↗