Membrane microviscosity and human platelet function

An increased sensitivity to epinephrine-induced aggregation has been observed both in platelets obtained from patients with type IIa hyperlipoproteinemia and in normal platelets following incubation with cholesterol-rich lecithin dispersions. We have reported previously that the membrane fraction of platelets is enriched with cholesterol relative to phospholipid under each of these conditions. To further explore the effect of cholesterol on platelet membranes, we have examined the fluidity (microviscosity) of whole platelets and platelet subcellular fractions using a hydrophobic fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene (DPH), under conditions in which the cholesterol-to-phospholipid mole ratio (C/PL) of platelets was varied by incubation with various cholesterol-lecithin sonicated dispersions. The C/PL of platelets directly influenced the rotational diffusion of DPH, as indicated by changes in fluorescence polarization. This was reflected in an increase in microviscosity at 37 degrees C (ETA37) from 2.84 P in normal platelets to 4.06 P in platelets with a 118% increase in C/PL. Conversely, platelets with a 43% decrease in C/PL had a 13% decrease in eta37. A strong correlation (r = 0.94) existed between C/PL and eta37 throughout this entire range. However, C/PL had no effect on the excited-state fluorescence lifetime of DPH. Both C/PL and eta37 were lower in isolated platelet membranes than in the platelet granule fraction. When platelets were incubated for 20 h with cholesterol-rich dispersions, there was an increase in C/PL and eta37 in both the membrane and granule fractions. However, this occurred more rapidly in membranes so that, at 5 h (a time when an increased sensitivity of whole platelets to epinephrine is evident), membrane C/PL had increased 55% and eta37 had increased 42%, whereas granule C/PL and eta37 had changed minimally. Cholesterol-rich platelets and subcellular fractions had a lower fusion (or flow) activation energy for viscosity (deltaE), reflecting a higher degree of order, and the converse was true in cholesterol-poor platelets. Moreover, a strong negative correlation existed between the percent change in deltaE and the percent change in eta37 induced either by cholesterol incorporation or depletion. These data demonstrate that cholesterol influences the fluidity and the degree of order within the hydrophobic core of platelet membranes. Changes induced in these physical properties by an excess of cholesterol relative to phospholipid may underlie the abnormal reception or transmission of the aggregation stimulus in cholesterol-rich platelets.     

Stereochemical requirements for intercalation of platinum complexes into double-stranded DNA's

The complexes 1,10-phenanthrolineethylenediamineplatinum(II) and 2,2'-bipyridineethylenediamineplatinum(II) have a planar, aromatic ligand system that facilitates intercalation, as shown by their ability to unwind closed circular duplex DNA. Nonbonded steric interactions can rotate the pryidine ligands out of the coordination plane in bis(pyridine)ethylenediamineplatinum(II), thus preventing intercalation. Fiber x-ray diffraction patterns of the two metallointeracalators indicate that the binding is governed by the neighbor exclusion principle.     

The wick catheter technique for measurement of intramuscular pressure. A new research and clinical tool

The wick catheter technique was developed in 1968 for measurement of subcutaneous pressure and has been modified for easy intramuscular insertion and continuous recording of interstitial fluid pressure in animals and humans. Studies in dogs of the anterolateral compartment of the leg in simulation of the compartment syndrome showed the technique to be accurate and reproducible. The wick catheter technique is capable of important clinical applications in the diagnosis and treatment of acute and chronic compartment syndromes.     

Bolus injection test for measurement of cerebrospinal fluid absorption

The significance of the bolus injection test lies in supplying data for evaluation of the cerebrospinal fluid (CSF) bulk flow. It provides pressure-time (PT) curves by the process of direct recording, while the pressure-volume (PV) and volume-time (VT) plots are subsequently computed...     

Comparative structural and immunochemical properties of leghaemoglobins

Circular dichroism studies on leghaemoglobins from snake bean, lupin, serradella and other plants show that, in common with soybean (reported earlier) they have a similar overall polypeptide chain conformation and haem environment and orientation. Immunochemical studies, on the other hand, suggest that the antigenic determinants on the surface of the leghaemoglobins vary considerably. Thus, firstly the alpha-helix content of the leghaemoglobins as a class is very similar (60-65%) and approaches that of the myoglobins, secondly, the sign, magnitude and shape of their circular dichroism spectra in the near ultraviolet, Soret and visible regions suggest close similarities in the environment and orientation of a structurally important tryptophan residue and of the haem moiety, and thirdly, there is comparatively weak haem-protein interaction. The extent of immuno cross-reactivity was found to be best deomonstrated using the Farr radioimmunoassay procedure. The results were (a) 5 leghaemoglobins from one plant (soybean) crossreacted completely but with varying affinities. (b) The extent of cross reactivity between leghaemoglobins from different plants was compared to that within a single plant; the reaction of antiserum to a soybean leghaemoglobin with a serradella leghaemoglobin was weak, with a snake bean leghaemoglobin still weaker (and incomplete) while lupin leghaemoglobins showed no cross reactivity at all. (c) The "rapid" attenuation of cross reactivity among different plant leghaemoglobins is explicable in terms of the extensive amino acid substitutions which have been demonstrated in the literature and in the present studies. (d) In view of this rapid divergence it is not surprising that sperm whale and horse heart myoglobins showed no cross reactivity with soybean leghaemoglobins. In summary, amino acid substitutions in the leghaemoglobin family are conformationally but not immunochemically conservative.     

Evolution and kinetics of monosaccharides,disaccharides and α-galactosides during germination of lentils

The effect of light and seed rinsing during the germination of lentil seeds (Lens culinaris var. vulgaris, cultivar Magda-20) on the level of monosaccharides, disaccharides and α-galactosides (raffinose, ciceritol and stachyose) was investigated. The total soluble sugar content corresponded to about 9% of the mature seed weight, about 65% of which was α-galactosides. Germination brought about a large decrease in α-galactosides: 18% to 40% losses after 3 days and 100% after 6 days. However, glucose, which was not detected in ungerminated seeds, as well as fructose and sucrose gradually increased during germination. The content of α-galactosides decreased more rapidly when germinating seeds were given 6 h light per day, but under these conditions there was also a major reduction in the levels of fructose, glucose and sucrose. Seeds rinsed daily showed a greater reduction of α-galactosides and an increase in the levels of fructose, glucose and sucrose. When seeds were germinated for 10 days in the dark with daily rinsing, the content of α-galactosides decreased gradually during the first 4 days and they were not detected after 6 days. Under these conditions, fructose, glucose and sucrose, which represented about 3% of the mature seed weight, started increasing after day 2 and represented more than 13% of the germinated seed dry weight after 10 days.     

Which smokers use the smoking cessation Quitline in Hong Kong,and how effective is the Quitline?

Objective: To describe the characteristics of the Chinese subjects who utilised the first telephone smoking cessation service in Hong Kong, and to evaluate its effectiveness.

Methods: The Quitline provided Hong Kong residents with free telephone smoking cessation services which was publicised through a press conference, media reports, pamphlets, and posters at public and private hospitals and clinics. Callers who completed an initial interview from 13 December 2000 to 31 May 2002 were included. Smokers were interviewed using a structured record sheet and provided with stage matched counselling. A follow up interview was carried out after six months. Analysis was conducted by intention-to-treat.

Results: Of the 1120 callers who completed initial assessments, 1047 were current smokers and 872 consented to follow ups. Compared to the general smoking population, the Quitline attracted more of those who were female, younger, single, unemployed, higher educated, smoking more than 20 cigarettes per day, and those with quitting experience. At six months, 12% (95% confidence interval 10% to 15%) of the participants reported that they had not smoked a cigarette for the past seven days. A stepwise logistic regression model showed that the use of nicotine replacement therapy at the present attempt to quit, having made one or more serious attempts to quit in the past, perceiving less difficulties in quitting, and smoking the first cigarette at age 15 years or above were significant predictors of quitting.

Conclusion: This first Quitline in Asia appears to be acceptable to Chinese smokers, with quit rate comparable to those of better funded Quitlines in the West. A low cost Quitline is a promising model for smoking cessation services in the East.

     

Assessment of empirical algorithms for bathymetry extraction using Sentinel-2 data

Bathymetry estimated from optical satellite imagery has been increasingly implemented as an alternative to traditional bathymetric survey techniques. The availability of new sensors such as Sentinel-2 with improved spatial and temporal resolution, in comparison with previous optical sensors, offers innovative capabilities for bathymetry derivation. This study presents an assessment of the fit between satellite data and the underlying models in the most widely used empirical algorithms: the linear band model and the log-transformed band ratio model using Sentinel-2A data. Both models were tested in two study areas of the Irish coast with different morphological and environmental conditions. Results showed that the linear band model fitted better than the log-transformed band ratio model providing coefficient of determination values, R², between 0.83 and 0.88 (0 m–10 m) for the five images considered in the study. The closest fit was found in the depth range 2 m–6 m. Atmospheric correction, bottom type influence, and water column conditions proved to be key factors in the bathymetric derivation using these satellite datasets.