Plasma membrane fluidity in isolated rat hepatocytes: comparative study using DPH and TMA-DPH as fluorescent probes

A novel micellar carrier to reverse multidrug resistance of tumours: TPGS derivatives with end-grafted cholesterol

D-α-tocopherol polyethylene glycol succinate (TPGS) has good biocompatibility, low immunogenicity, prolonged circulation time, and it can reverse multidrug resistance of tumours. However, the micelle concentration (CMC) of TPGS is too high (0.2 mg/mL) to develop the formulation of the micelle. In this study, TPGS was modified with cholesterol to obtain a new carrier material, TPGS-CHMC. The CMC of TPGS-CHMC was 2 μg/mL, which was extremely lower than that of TPGS. Docetaxel (DTX)-loaded TPGS-CHMC micelles (TPGS-CHMC/DTX) exhibited an average size of approximately 13 nm, a zeta potential of approximately -4.66 mV, and high encapsulation efficiency (99.2 ± 0.6%). TPGS-CHMC reduced mitochondrial membrane potential and cell membrane fluidity in paclitaxel-resistant ovarian cancer cells (A2780/T). In vivo, DiR-loaded TPGS-CHMC micelles were selectively distributed in A2780/T tumour-bearing nude mice. In A2780/T tumour-bearing nude mice, TPGS-CHMC/DTX micelles displayed significantly higher anti-tumour activity and less toxicity than the free DTX solution. In summary, TPGS-CHMC has various advantages, and provides a new option for developing functional polymeric micelles.

Mechanism of the chilling-induced decrease in proton pumping across the tonoplast of rice cells

The ATP-generated proton pumping across tonoplast vesicles from chilling-sensitive Boro rice (Oryza sativa L. var. Boro) cultured cells was markedly decreased by chilling at 5 degrees C for 3 d. The membrane fluidity of core hydrophobic and surface hydrophilic regions of the lipid bilayer was measured by steady-state fluorescence depolarization of 1,6-diphenyl-1,3,5-hexatriene and trimethylammonium 1,6-diphenyl-1,3,5-hexatriene and by electron spin resonance spectroscopy of 16- and 5-doxyl stearic acid, respectively. The fluidity of the surface region of the lipid bilayer of the tonoplast vesicles decreased by chilling. The fluidity of the surface region of the liposomes and the proton pumping across the reconstituted proteoliposomes with tonoplast H+-ATPase decreased with increasing content of the glycolipids. The proton pumping across chimera proteoliposomes was reduced by chilling only when it was reconstituted in the presence of tonoplast glycolipids from chilled Boro cells. These data suggest that the reduction in ATP-generated proton pumping across the tonoplast by chilling is due to the decrease in the fluidity of the surface region of the lipid bilayer of the tonoplast, which is caused by the changes in glycolipids.

Cheek cell membrane fluidity measured by fluorescence recovery after photobleaching and steady-state fluorescence anisotropy

Membrane fluidity of human cheek cells was determined using fluorescence recovery after photobleaching (FRAP) and steady-state fluorescence anisotropy. The FRAP data showed that the lateral diffusion coefficient (D) and mobile fraction (%R) of lipid in the plasma membrane of control cells were 2.01 x 10(-9) cm2/sec and 54.25%, respectively. Trypsin treatment increased D and %R to 6.4 x 10(-9) cm2/sec and 72.15%. In contrast, the anisotropy (r) for control cells was 0.270 which remained unchanged by trypsin treatment. The results show that diffusion of lipids in the plane of the membrane is restricted by trypsin-sensitive barriers.

Membrane heterogeneity in isolated rat hepatocytes and liver plasma membrane subfractions: a comparative study using DPH and its cationic derivative TMA-DPH

The fluorescence decay of 1,6-diphenyl-1,3,5-hexatriene (DPH) and of 1-(4-trimethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) has been studied in hepatocytes isolated from rat liver and in isolated plasma membrane subfractions (cLPM, canalicular membranes and bLPM, basolateral membranes) using frequency domain fluorometry. The decay has been analyzed either by using a model of discrete exponential components or a model that assumes a continuous distribution of lifetime values in order to study different aspects of membrane heterogeneity. The results obtained by the two analyses are practically superimposable but the distributional approach allows an evaluation of membrane heterogeneity through the width of the distribution that has shown particularly significant differences when freshly hepatocytes are compared with in vitro aged hepatocytes. Moreover, the comparison of the distributional analysis of the two probes has shown in cLPM a tendency to higher values of the main lifetime component and a narrower distribution width with respect to bLPM. These results indicate changes of membrane domain organization that have been discussed in relation with the specific lipid composition that characterizes the two membrane subfractions. Our results indicate that frequency domain fluorometry may be used to study membrane heterogeneity in intact cells and isolated membranes.

The plasma-membrane internalization and recycling is enhanced in macrophages upon activation with gamma-interferon and lipopolysaccharide; a study using the fluorescent probe trimethylaminodiphenylhexatriene

The lipophilic fluorescent probe trimethylaminodiphenylhexatriene (TMA-DPH), previously used as a plasma membrane marker in membrane fluidity and exocytosis studies, was shown, to monitor the plasma-membrane internalization-recycling shuttle movement in cells. Using this approach we present here kinetic and dose-response data, which give evidence that the plasma membrane flow is enhanced in bone marrow macrophages from various mouse strains, upon in vitro activation with gamma interferon (IFN-gamma) or bacterial lipopolysaccharide (LPS), within physiological dose ranges. The effect studied evolved in line with the usual development kinetics of macrophage activation. Complementary assays on membrane fluidity, surface charge density and membrane surface indicated no related changes. From these experiments it is concluded that the observed enhancement of the plasma membrane traffic does not originate from specific limited membrane modifications, but is merely a particular feature of the overall macrophage activation.

Evidence that plasma membrane fluidity of isolated hepatocytes is modified by exposure to microtubule-depolymerizing drugs

The role of microtubules on membrane fluidity has been investigated on freshly isolated whole rat hepatocytes prepared by the perfusion method and exposed either to the microtubule-depolymerizing drugs colchicine and vincristine or to beta-lumicolchicine, a colchicine analog deprived of biological activity. Exposure of hepatocytes to 6.3 microM colchicine or to 3.0 microM vincristine led to a significant decrease of membrane fluidity as measured by fluorescence polarization of trimethylammoniodiphenylhexatriene (TMA-DPH). No changes were observed in cells exposed to 10.0 microM beta-lumicolchicine. These observations support the hypothesis that the microtubular system plays a role in the modulations of physico-chemical properties of the plasma membrane.