Biomedical subjects

K H Cheng

Publications and source records attributed to K H Cheng.

At least 19 recordsLinked to original sources

PubMed1997

Evidence for superlattice arrangements in fluid phosphatidylcholine/phosphatidylethanolamine bilayers.

Recently, evidence for cholesterol and phosphatidylcholine (PC) molecules to adapt superlattice arrangements in fluid lipid bilayers has been presented. Whether superlattice arrangements exist in other biologically relevant lipid membranes, such as phosphatidylethanolamine (PE)/PC, is still speculative. In this study, we have examined the physical properties of fluid 1-palmitoyl-2-oleoyl-PC (POPC) and 1-palmitoyl-2-oleoyl-PE (POPE) binary mixtures as a function of the POPE mole fraction (X(PE)) using fluorescence and Fourier transform infrared spectroscopy. At 30 degrees C, i.e., above the Tm of POPE and POPC, deviations, or dips, as well as local data scattering in the excimer-to-monomer fluorescence intensity ratio of intramolecular excimer forming dipyrenylphosphatidylcholine probe in POPE/POPC mixtures were detected at X(PE) approximately 0.04, 0.11, 0.16, 0.26, 0.33, 0.51, 0.66, 0.75, 0.82, 0.91, and 0.94. The above critical values of X(PE) coincide (within +/-0.03) with the critical mole fractions X(HX,PE) or X(R,PE) predicted by a headgroup superlattice model, which assumes that the lipid headgroups form hexagonal or rectangular superlattice, respectively, in the bilayer. Other spectroscopic data, generalized polarization of Laurdan and infrared carbonyl and phosphate stretching frequency, were also collected. Similar agreements between some of the observed critical values of X(PE) from these data and the X(HX,PE) or X(R,PE) values were also found. However, all techniques yielded critical values of X(PE) (e.g., 0.42 and 0.58) that cannot be explained by the present headgroup superlattice model. The effective cross-sectional area of the PE headgroup is smaller than that of the acyl chains. Hence, the relief of "packing frustration" of PE in the presence of PC (larger headgroup than PE) may be one of the major mechanisms in driving the PE and PC components to superlattice-like lateral distributions in the bilayer. We propose that headgroup superlattices may play a significant role in the regulation of membrane lipid compositions in cells.

Biophysical Phenomena↗

PubMed1997

An experimental method for measuring aerosol deposition efficiency in the human oral airway.

An experimental technique was developed to measure the oral deposition of aerosols by successively drawing them passively through (1) the nasal and oral passage in series, and (2) the nose and an oral bypass "extension tube" inserted into the oral cavity just anterior to the uvula. To test this technique, a replicate human upper airway cast was challenged with monodisperse aerosols ranging in diameter from 3.6 to 150.0 nm at constant flow rates ranging from 7.5 to 30 L/min. For the inhalation study, test aerosols were drawn into the nasal cavity and directed either through the laryngeal-tracheal (L-T) section or the oral passage with/without the oral extension tube. The flow was reversed for the exhalation study. Deposition fractions of aerosols in the main oral cavity were found approximately equal to those in the L-T section for both inhalation and exhalation. Following this phase of the study, experimental measurements of total particle deposition fraction for the oral inlet-tracheal outlet path were performed. The results of these measurements agreed well with the calculated oral deposition fractions based on the initial measurements. This technique has application for measuring oral deposition of larger particles encountered in occupational environments.

Aerosols↗

PubMed1997

Measurements of airway dimensions and calculation of mass transfer characteristics of the human oral passage.

This paper presents measurements of the geometric shape, perimeter, and cross-sectional area of the human oral passage (from oral entrance to midtrachea) and relates them through dimensionless parameters to the depositional mass transfer of ultrafine particles. Studies were performed in two identical replicate oral passage models, one of which was cut orthogonal to the airflow direction into 3 mm elements for measurement, the other used intact for experimental measurements of ultrafine aerosol deposition. Dimensional data were combined with deposition measurements in two sections of the oral passage (the horizontal oral cavity and the vertical laryngeal-tracheal airway) to calculate the dimensionless mass transfer Sherwood number (Sh). Mass transfer theory suggests that Sh should be expressible as a function of the Reynolds number (Re) and the Schmidt number (Sc). For inhalation and exhalation through the oral cavity (O-C), an empirical relationship was obtained for flow rates from 7.5-30.0 1 min-1: Sh = 15.3 Re0.812 Sc-0.986 An empirical relationship was likewise obtained for the laryngeal-tracheal (L-T) region over the same range of flow rates: Sh = 25.9 Re0.861 Sc-1.37 These relationships were compared to heat transfer in the human upper airways through the well-known analogy between heat and mass transfer. The Reynolds number dependence for both the O-C and L-T relationships was in good agreement with that for heat transfer. The mass transfer coefficients were compared to extrathoracic uptake of gases and vapors and showed similar flow rate dependence. For gases and vapors that conform to the zero concentration boundary condition, the empirical relationships are applicable when diffusion coefficients are taken into consideration.

Absorption↗

PubMed1996

Detection of membrane packing defects by time-resolved fluorescence depolarization.

Packing defects in lipid bilayer play a significant role in the biological activities of cell membranes. Time-resolved fluorescence depolarization has been used to detect and characterize the onset of packing defects in binary mixtures of dilinoleoylphosphatidylethanolamine/1-palmitoyl-2- oleoylphosphatidylcholine (PE/PC). These PE/PC mixtures exhibit mesoscopic packing defect state (D), as well as one-dimensional lambellar liquid crystalline (L alpha) and two-dimensional inverted hexagonal (HII) ordered phases. Based on previous electron microscopic investigations, this D state is characterized by the presence of interlamellar attachments and precursors of HII phase between the lipid layers. Using a rotational diffusion model for rod-shaped fluorophore in a curved matrix, rotational dynamics parameters, second rank order parameter, localized wobbling diffusion, and curvature-dependent rotational diffusion constants of dipyenylhexatriene (DPH)-labeled PC (DPH-PC) in the host PE/PC matrix were recovered from the measured fluorescence depolarization decays of DPH fluorescence. At approximately 60% PE, abrupt increases in these rotational dynamics parameters were observed, reflecting the onset of packing defects in the host PE/PC matrix. We have demonstrated that rotational dynamics parameters are very sensitive in detecting the onset of curvature-associating packing defects in lipid membranes. In addition, the presence of the D state can be characterized by the enhanced wobbling diffusional motion and order packing of lipid molecules, and by the presence of localized curvatures in the lipid layers.

Cell Membrane↗

PubMed1996

Effects of unsaturation and curvature on the transverse distribution of intramolecular dynamics of dipyrenyl lipids.

The roles of acyl chain unsaturation and curvature in the excimer formation efficiency (EFE) of site-specific conjugated pyrene molecules in lipid membranes have been investigated by steady-state and time-resolved fluorescence spectroscopy. Six 1-2-(pyrenyl-n-acyl)-phosphatidylcholine (dipy(n)PC) probes, with pyrenyl chains of varying methylene units n from 4 to 14 carbons, were incorporated separately into dioleoylphosphatidylcholine (DOPC) or dioleoylphosphatidylethanolamine (DOPE) lipid membranes at 0.1 mol%. Both the excimer-to-monomer fluorescence intensity ratio and association-to-dissociation rate constant ratio of conjugated pyrenes were used to quantify EFE. At all temperatures (T = 0-30 degrees C) and for n = 4 and 6, the EFE for DOPE was always smaller than EFE for DOPC. At T < 10 degrees C (where DOPE and DOPC are in the liquid crystalline L alpha phase) and for n > 8, the EFE for curvature frustrated DOPE was significantly greater than EFE for nonfrustrated DOPC (control), and the difference increased gradually with n. At T> 18 degrees C (where DOPE is in the inverted hexagonal H(II) phase and DOPC is in the L alpha phase) and for n > 8, EFE for the curvature-relaxed DOPE was again smaller than the EFE for DOPC control. The contributions of splay conformation and internal dynamics of pyrenyl chains to EFE were examined separately using a lattice model. Our results suggest that i) the cis double bonds of the host lipid matrix strongly perturb both the conformation and dynamics of conjugated pyrenes at the specific location around n = 8, and ii) the lateral stress at the upper part (n < 8) of the curvature frustrated bilayer membranes (DOPE) may be significantly relaxed once the membrane surface adopts a favorable negative interfacial curvature.

Kinetics↗

PubMed1996

Immunoglobulin A antibodies against Pseudomonas aeruginosa in the tear fluid of contact lens wearers.

PURPOSE: Pseudomonas aeruginosa is the most important cause of contact lens-associated ulcerative keratitis, especially for those who use extended-wear lenses. Until now, the presence of specific anti-P. aeruginosa immunoglobulin A (IgA) antibodies in the tears of contact lens wearers has not been investigated and is the purpose of the current study. METHODS: The levels of specific IgA antibodies against P. aeruginosa and total secretory IgA (s-IgA) concentrations were measured in tears of various groups of contact lens and non-contact lens wearers using enzyme-linked immunosorbent assays. Contact lens groups were divided into the following categories: daily-wear rigid gas-permeable lenses (n = 23), daily-wear soft lenses (n = 22), extended-wear soft lenses (n = 17), and non-contact lens wearers (n = 23). As a positive control group, we tested tears obtained from patients with cystic fibrosis (n = 5) because the respiratory tract of these persons often are colonized by P. aeruginosa. RESULTS: The percentage of nonresponders (< 15 U/ml) varied between 9% in daily-wear rigid gas-permeable contact lens users to 23% in daily-wear soft contact lens users. The percentage of nonresponders in controls was 13%. The frequency of nonresponders was not significantly different among the different groups tested. All patients with cystic fibrosis showed a very high anti-P. aeruginosa IgA response in their tears. When analyzing the mean anti-P. aeruginosa IgA response, a significantly lower level was found in extended-wear contact lens users (38 U/ml) compared to non-contact lens wearers (82 U/ml). Total s-IgA levels in the tears of the various groups tested were not significantly different. CONCLUSIONS: A substantial number of persons in the population of contact lens wearers tested lack detectable IgA antibodies against P. aeruginosa in their tears and may be susceptible to P. aeruginosa keratitis if the physiological condition of their cornea is compromised.

Adolescent↗

PubMed1995

Sidestream tobacco smoke exposure acutely alters human nasal mucociliary clearance.

Nasal mucociliary clearance (NMC) is a biomarker of nasal mucosal function. Tobacco smokers have been shown to have abnormal NMC, but the acute effect of environmental tobacco smoke (ETS) on nonsmokers is unknown. This study evaluated acute tobacco smoke-induced alterations in NMC in 12 healthy adults. Subjects were studied on 2 days, separated by at least 1 week. Subjects underwent a 60-min controlled exposure at rest to air or sidestream tobacco smoke (SS) (15 ppm CO) in a controlled environmental chamber. One hour after the exposure, 99mTc-sulfur colloid was aerosolized throughout the nasal passage and counts were measured with a scintillation detector. Six out of 12 subjects showed more rapid clearance after smoke exposure than after air exposure, and 3/12 had rapid clearance on both days. However, substantial decreases in clearance occurred in 3/12 subjects, all of whom had a history of ETS rhinitis. In two subjects, more than 90% of the tracer remained 1 hr after tracer administration (2 hr after smoke exposure). Understanding the basis for biologic variability in the acute effect of tobacco smoke on NMC may advance our understanding of pathogenesis of chronic effects of ETS.

Adult↗

PubMed1994

Detection and characterization of the onset of bilayer packing defects by nanosecond-resolved intramolecular excimer fluorescence spectroscopy.

Bilayer packing defects in binary dilinoleoylphosphatidylethanolamine and 1-palmitoyl-2-oleoylphosphatidylcholine (DLPE/POPC) lipid mixtures have been studied by the use of nanosecond-resolved intramolecular excimer fluorescence spectroscopy. Frequency-domain fluorescence intensity decays of dual-chain labelled dipyrenyl lipids of different chain lengths in DLPE/POPC mixtures were acquired at both the monomer (392 nm) and excimer (475 nm) emission channels and at 20 degrees C. On the basis of a new intramolecular excimer formation kinetic model, the extent of aggregation and the rotational mobility, in terms of the equilibrium constant of the monomer to aggregated state and the excimer association rate constant, respectively, of the intralipid pyrenes were calculated from the frequency-domain data. Within the range of 60-100% DLPE where bilayer defects are known to coexist with bilayer and non-bilayer states, a prominent peak in the equilibrium constant and a concomitant dip in the excimer association constant at approximately 80% DLPE were observed. Our nanosecond-resolved fluorescence results suggest that the intramolecular excimer kinetic parameters of dipyrenyl lipids are very sensitive to the onset of bilayer packing defects in lipid membranes. Moreover, the onset of bilayer defect state is characterized by the greater extent of aggregation and more hindered rotational mobility of the acyl chains as compared with the bilayer (0% DLPE) and non-bilayer inverted hexagonal (100% DLPE) states of the lipid membranes.

Kinetics↗

PubMed1994

Infrared study of the bilayer stability behavior of binary and ternary phospholipid mixtures containing unsaturated phosphatidylethanolamine.

The bilayer stability of liposomes containing unsaturated phosphatidylethanolamine (PE) has been investigated by measuring the C = O and CH2 stretching frequencies of the lipids at different lipid compositions and temperatures. Binary mixtures of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and dilinoleoyl-PE (DLPE) are known to exhibit lamellar liquid crystalline (L alpha), inverted hexagonal (HII) and metastable intermediate (I) phases. Abrupt increases in the C = O and CH2 stretching frequencies at 65-75 and 90-95% PE, respectively, were found as the PE content of the DLPE/POPC mixtures was increased from 0 to 100%. These transitions were associated with the L alpha -I and I-HII phase transitions of the DLPE/POPC mixtures, accordingly. The effects of three lipid perturbants, butylated hydroxytoluene (BHT), diacylglycerol (DG) and cholesterol (CL), on the above L alpha -I and I-HII transitions were also examined. All perturbants were found to be effective in shifting the L alpha -I transition of the DLPC/POPC mixtures to a lower PE% as detected by the C = O stretching frequency measurements. On the other hand, the perturbants appeared to eliminate the I-HII transition of the DLPE/POPC mixtures as detected by the CH2 stretching frequency measurements. The effectiveness of the perturbants in promoting the L alpha -I phase transition of the DLPE/POPC mixtures followed the order of DG > BHT > CL.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid Bilayers↗

PubMed1994

In vivo tissue characterization of human brain by chisquares parameter maps: multiparameter proton T2-relaxation analysis.

The heterogeneous proton MR relaxation decay process in human brain has been investigated by performing region-of-interest and pixel-by-pixel calculations on the multiecho MR images with different repetition times (TR) of human brains using a clinical 1.5-T whole-body superconducting MR scanner. Based on the monoexponential, biexponential, and continuous gaussian distribution relaxation models, first-order proton relaxation parameters (proton density, T1 and T2) and higher-order transverse proton relaxation parameters (T2-long, T2-short, T2-long fraction, T2-average, and T2-distribution width) were calculated. On the basis of an F test (p < .01), the statistical significance of the higher-order (biexponential and distribution) fits over the monoexponential fit was evaluated. Here, a significant improvement in the biexponential fit was found for some of the regions containing the ventricular cerebrospinal fluid (CSF) (T2-long = 2780 +/- 570 ms; T2-short = 159 +/- 42 ms; T2-long fraction = 0.51 +/- 0.08 ms) due to the partial volume effect but not for most of the white matter (WM). On the other hand, an improvement of fit to WM was obtained when distribution (T2-average = 80 +/- 8 ms; T2-distribution half-width = 21 +/- 4 ms) as opposed to monoexponential (T2 = 89 +/- 10 ms) fit was used. As internal controls, tubes of CuSO4 solution (T2 = 1293 +/- 128 ms) and agarose gel (T2 = 111 +/- 10 ms) which have similar T2 values as the CSF and WM of the brain, respectively, were attached to the human head and imaged concomitantly. No significance improvements in either the biexponential or distribution fits over the monoexponential fit were found for all the controls. In addition to the first-order and higher-order relaxation parameter maps, the monoexponential chisquares, as well as the chisquares ratio (chisquares of the monoexponential fit divided by that of the higher-order fit), maps were also generated. Unlike the higher-order T2-relaxation parameter maps, the chisquares parameter maps required no selection of any predetermined statistical confidence level. Therefore, these chisquares parameter maps provided a somewhat nonsubjective spatial profile of the heterogeneous transverse relaxation process in the brain. Our results led us to propose that the use of chisquares parameter maps, together with the first-and higher-order relaxation parameter maps, may further improve the in vivo tissue characterization capability of MRI in future clinical diagnosis and staging of intracranial diseases.

Adult↗

PubMed1994

Intramolecular excimer kinetics of fluorescent dipyrenyl lipids: 1. DMPC/cholesterol membranes.

The intramolecular dynamics of the excimer forming dipyrenyl lipids (DipynPC) of different chain lengths (n) in ethanol and in dimyristoylphosphatidycholine (DMPC) membranes was investigated by the use of frequency-domain fluorescence intensity decay technique. Based on a 3-state model, the extent of aggregation and rotational rate of the two intralipid pyrene moieties in the dipyrenyl lipids were estimated from the frequency-domain data. In ethanol (20 degrees C), the rotational rate for DipynPC increased progressively as n was varied from 4 to 12. At the gel (L beta)-to-liquid crystalline (L alpha) phase transition of DMPC (approximately 23 degrees C), the rotational rate increased and aggregation decreased significantly for Dipy10PC, whereas only the rotational rate was changed for Dipy4PC. In the presence of 30 mol% cholesterol, significant increases in both the rotational rate and aggregation were observed for Dipy10PC in both L beta and L alpha phases. However, for the case of Dipy4PC, an increase in the rotational rate but a decrease in the aggregation were noticed only in the L beta phase, and no similar changes were detected in the L alpha phase. Our results indicate differential effects of cholesterol on the conformational dynamics of acyl chains at different depths of the membranes.

Cholesterol↗

PubMed1994

Intramolecular excimer kinetics of fluorescent dipyrenyl lipids: 2. DOPE/DOPC membranes.

The intramolecular dynamics of the excimer-forming dipyrenyl lipids (DipynPE) of different chain lengths (n) in fully hydrated dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC) binary mixtures was investigated by the use of frequency-domain fluorescence intensity dcay technique. Using a 3-state model (see companion paper), the extent of aggregation and rotational rate of the two covalently attached pyrene moieties in DipynPE were estimated from the frequency-domain data. At 1 degrees C, the rotational rate and aggregation for Dipy4PE and Dipy10PE were insensitive to DOPE% of the lipid bilayer. At 27 degrees C, the rotational rate decreased, whereas the aggregation increased steadily for Dipy10PE as the DOPE% of the bilayer increased from 0 to 80. However, an abrupt increase in the rotational rate and a decrease in the aggregation for Dipy10PE were detected as the DOPE% reached 100, at which point the membranes are in the inverted hexagonal (HII) phase. No similar changes were found for Dipy4PE. These results indicate that the presence of PE with large intrinsic-curvature increases the lateral stress at the region near the center of the bilayer, and that this stress can be relieved as the membranes enter the highly curved HII phase.

Kinetics↗

PubMed1993

Quantitation of non-Einstein diffusion behavior of water in biological tissues by proton MR diffusion imaging: synthetic image calculations.

The non-Einstein diffusion behavior of water in a model biological tissue system, intact duck embryos, has been investigated by the use of an in vivo proton pulsed-gradient spin-echo (PGSE) MR imaging technique. Multiple-frame MR images of the intact duck embryos and control solution (0.5 mM CuSO4 doped water) were acquired systematically at different diffusion times and strengths of the diffusion-sensitizing magnetic field gradients of the PGSE sequence. These raw images were then used to generate various dynamic (self-diffusion coefficient) and structural (fractal, residual attenuation, and compartment fraction) diffusion parameter maps of water in the imaging objects on the basis of different Einstein and higher order (non-Brownian, Residual, and 2-compartment) diffusion models. The self-diffusion coefficients of the body tissues of the embryos obtained from all diffusion models were significantly lower than those of the surrounding embryonic fluid. The structural diffusion parameter maps obtained from the higher order diffusion models revealed that water molecules exhibited either non-Brownian, restricted, or compartmentalized diffusion behavior in the embryonic tissues, but Einstein or Brownian diffusion behavior in the embryonic fluid and control solution. The diffusion parameter maps, both dynamic and structural, were found to provide much better contrasts than the conventional relaxation time (T1, T2, and biexponential T2) maps in separating the tissues from the surrounding embryonic fluid in the duck embryos. The mathematical models and procedures for generating the dynamic and structural diffusion parameter maps are also presented in this paper.

Animals↗

PubMed1993

Transjugular intrahepatic portosystemic shunt. Requiem for the surgical portosystemic shunt?

Is transjugular intrahepatic portosystemic shunt (TIPS) preferable to a surgical shunting procedure in patients who are expected to benefit from a portal-systemic shunt? Since randomized trials comparing these procedures have not yet been reported, we attempted to define the present best therapeutic strategy by reviewing both the recent literature on TIPS and surgical shunting and our first experience with TIPS. The results suggest that TIPS is just as effective as surgical shunting but is associated with a lower morbidity and mortality. Procedure related deaths seem rare. In our series of 16 patients there was one death within 30 days. Seven early complications including stent dislodgement, early occlusion, encephalopathy and haemolysis were noted. The incidence of long-term complications, especially encephalopathy and shunt occlusion, seems comparable for both shunting procedures. Major advantages of TIPS are its therapeutic efficacy in patients with ascites and the fact that the technical difficulties of performing liver transplantation are not increased. We conclude that TIPS, performed by an experienced team, is at present the procedure of choice in patients who are candidates for a portal-systemic shunt, especially in patients in whom liver transplantation is a future option. Surgical shunts can be reserved for patients in whom TIPS is not feasible or has failed.

Ascites↗

PubMed1992

Magnetic resonance diffusion imaging detects structural damage in biological tissues upon hyperthermia.

The use of quantitative nuclear magnetic resonance (MR) imaging to investigate the extent and mechanism of hyperthermic damage in biological tissues has been studied. By using the multiple delay-multiple echo and pulsed-gradient spin echo MR imaging sequences, multiple frame MR images of freshly harvested rabbit tissues (brain, kidney, and muscle) and intact duck embryos in shells were obtained before and after heat treatment (45 degrees C for 30 min) using a clinical 1.5-Tesla whole-body superconducting MR scanner. Based on the relaxation and diffusion models, maps of the proton spin density, relaxation times, and various self-diffusion parameters of tissue water were generated from these multiple frame MR images. Our results indicated that the values of the diffusion barrier size and fractal parameter of the tissues and the self-diffusion coefficient of tissue water increased significantly, i.e., approached that of free water, after the heat treatment. In comparison, only slight changes in the spin density and relaxation times of the tissue water were found after the identical heat treatment. We concluded that the significant changes in the self-diffusive behavior of the tissue water are due to the denaturation of macromolecules (e.g., protein and fiber) within the tissues at elevated temperatures. We further suggested that MR diffusion imaging represents a powerful tool to investigate the extent and mechanism of heat damage of biological tissues in vivo and therefore bears important potential in the clinical assessment of the therapeutic efficacy of hyperthermia in cancer therapy.

Animals↗

PubMed1992

Inactivation of calcium uptake by EGTA is due to an irreversible thermotropic conformational change in the calcium binding domain of the Ca(2+)-ATPase.

Calcium uptake by rabbit skeletal sarcoplasmic reticulum (SR) is inhibited with an effective inactivation temperature (TI) of 37 degrees C in EGTA with no effect on ATPase activity. Since the Ca-ATPase denatures at a much higher temperature (49 degrees C) in EGTA, this suggests that a small or localized conformational change of the Ca-ATPase at 37 degrees C results in inability to accumulate calcium by the SR. Using a fluorescent analogue of dicyclohexylcarbodiimide, N-cyclohexyl-N'-[4-(dimethylamino)-alpha-naphthyl]-carbodiimide (NCD-4), the region of the calcium binding sites of the SR Ca-ATPase was labeled. Steady-state and frequency-resolved fluorescence measurements were subsequently performed on the NCD-4-labeled Ca-ATPase. Site-specific information pertaining to the hydrophobicity and segmental flexibility of the region of the calcium binding sites was derived from the steady-state fluorescence intensity, lifetime, and rotational rate of the covalently bound NCD-4 label as a function of temperature (0-50 degrees C). A reversible transition at approximately 15 degrees C and an irreversible transition at approximately 35 degrees C were deduced from the measured fluorescence parameters. The low-temperature transition agrees with the previously observed break in the Arrhenius plot of ATPase activity of the native Ca-ATPase at 15-20 degrees C. The high-temperature transition conforms well with the conformational transition, resulting in uncoupling of Ca translocation from ATP hydrolysis as predicted from the irreversible inactivation of Ca uptake at 31-37 degrees C in 1 mM EGTA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Quantitation of lateral stress in lipid layer containing nonbilayer phase preferring lipids by frequency-domain fluorescence spectroscopy.

Frequency-resolved fluorescence measurements have been performed to quantitate the lateral stress of the lipid layer containing nonbilayer phase preferring dioleoylphosphatidylethanolamine (DOPE). On the basis of a new rotational diffusion model, the wobbling diffusion constant (Dw), the curvature-related hopping diffusion constant (DH), and the two local orientational order parameters ([P2] and [P4]) of 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl] carbonyl]-3-sn-phosphatidylcholine (DPH-PC) in fully hydrated DOPE and DOPE/dioleoylphosphatidylcholine (DOPC) mixtures were calculated from the frequency-domain anisotropy data. The values of [P2], [P4], and DH for DOPE were found to increase significantly at approximately 12 degrees C, the known lamellar liquid crystalline (L alpha) to inverted hexagonal (HII) phase transition temperature of DOPE. Similar features as well as a decline of Dw were detected in the DOPE/DOPC mixtures as the DOPE content was increased from 85% to 90% at 23 degrees C, corresponding to the known lyotropic phase transition of the DOPE/DOPC. In contrast, for DOPC (0-40 degrees C) and DOPE/DOPC (0-100% DOPE at 3 degrees C), which remained in the L alpha phase, these changes were not detected. The most probable local orientation of DPH-PC in the DOPE/DOPC mixtures shifted progressively toward the normal of the lipid/water interface as the content of DOPE increased. We concluded that the curvature-related lateral stress in the lipid layer increases with the content of the nonbilayer phase preferring lipids.

Diffusion↗

PubMed1992

Activation energy and entropy for intramolecular excimer formation in a dipyrenylphosphatidylcholine probe in lamellar and hexagonal lipid phases.

Intramolecular excimer formation in pyrene-labeled phosphatidylcholine was used as a tool to determine thermodynamic characteristics of the lamellar to hexagonal phase transitions in a binary lipid system dilinoleoylphosphatidylethanolamine (DLPE)/palmitoyloleoylphosphatidylcholine (POPC). Upon an L alpha/HII phase transition, the activation energy Ea for excimer formation increased from 5.6 +/- 0.2 kcal/mol to 6.3 +/- 0.2 kcal/mol, while the activation entropy delta S decreased from -40.0 +/- 0.8 cal/K.mol to -38.4 +/- 0.8 cal/K.mol. The results are consistent with the idea of molecular splaying of the acyl chains in the hexagonal phase. It is estimated that the molecular area at the terminal carbon of the lipid acyl chains increases by a factor of 2.2 upon the L alpha HII transition in DLPE/POPC.

Lipids↗