Single Particle Population Research Articles

The isolation, characterisation and quantification of the equine plasma lipoproteins

Plasma lipoproteins were isolated from eight Thoroughbred horses and eight Shetland ponies on the basis of particle size by gel filtration chromatography and according to density using rate-zonal ultracentrifugation. Three major classes corresponding to very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) were identified and characterised by their lipid and apolipoprotein compositions. The particle size distributions of each class were determined by electron microscopy and non-denaturing polyacrylamide gradient gel electrophoresis. HDL was found to dominate the equine lipoprotein spectrum, accounting for 61 per cent of the total plasma lipoprotein mass (VLDL 24 per cent, LDL 15 per cent). The VLDL class was isolated as a single population of particles that were triglyceride rich and cholesterol, phospholipid and protein poor. Equine LDL was characteristically cholesterol rich and was found to be polydisperse comprising three subfractions that were discrete with respect to particle size and lipid composition. The HDL class was composed of homogeneous particles that were typically protein rich. Apolipoprotein (apo) B was the major protein of VLDL and LDL, and presented two components on polyacrylamide gel electrophoresis with molecular weights in the region of human apoB-100 and a third in VLDL similar to that of apoB-48. ApoA-I was the predominant protein in equine HDL. Although there were no breed differences in the physical or chemical properties of each lipoprotein class, the Shetland ponies had higher plasma triglyceride and VLDL concentrations than their Thoroughbred counterparts.

Expression of human apolipoprotein A-I in transgenic mice results in reduced plasma levels of murine apolipoprotein A-I and the appearance of two new high density lipoprotein size subclasses.

In Western societies high density lipoprotein (HDL) levels correlate inversely with the risk for coronary heart disease. The primary protein component of both human and mouse HDL is apolipoprotein A-I (apoAI), which comprises greater than 70% of HDL protein and 30% of HDL mass. Human HDLs include particles of several distinct size subpopulations, whereas HDLs from inbred C57BL/6 mice contain a single population of particles. To study the regulation of apoAI expression and its role in HDL assembly, we created transgenic C57BL/6 mice containing the human apoAI gene. Two independent lines of transgenic mice with approximately twice the normal plasma levels of total apoAI were studied. The level of mouse apoAI is reduced greater than 4-fold in both transgenic lines, comprising only 4% of total plasma apoAI levels in one transgenic line and 13% in the other. We demonstrate that the mechanism responsible for the decrease in mouse apoAI is posttranscriptional. Parallel to the replacement of mouse with human apoAI, the single HDL species normally present in the plasma of C57BL/6 is replaced by two HDL subclasses similar in size to human HDL2b and HDL3a. The changes in murine apolipoprotein levels and HDL subclass size are inherited by all transgenic offspring of the two founder animals. These results suggest a dominant role of apoAI in determining the HDL particle size distribution and a mechanism involving expression of human apoAI transgenes that alters the plasma levels of mouse apoAI.

An optical synchrotron nebula around the X-ray pulsar 0540 693 in the Large Magellanic Cloud

The discovery of extended optical continuum emission around the recently discovered 50 ms X-ray pulsar in the supernova remnant 0540 - 693 is reported. Exposures in blue and red broad-band filters made with the CTIO 4 m telescope and prime focus CCD show a center-brightened but clearly extended nebula about 4 arcsec in diameter (FWHM), while an image in an (O III) filter shows an 8 arcsec diameter shell (as reported earlier) which encloses the continuum source. The extinction-correction magnitudes B = 17.5 and I = 16.4 both correspond to flux densities which lie directly on the extrapolation of the observed X-ray power-law spectrum, suggesting that the emission from 10 to the 14.5 Hz to 10 to the 18th Hz is synchrotron radiation from a single population of particles. Line emission is shown to be only a small contaminant in the broad-band images. Thus the 0540 - 693 system is apparently a very close analog of the Crab Nebula. Any point source component in the former nebula must have B greater than 20; the Crab pulsar at this distance would have B approximately 23. The implications of the observations for the energetics of the pulsar/nebula system are discussed.

A subcellular pool of hypo-osmotically resistant particles containing thyrotropin releasing hormone, alpha-melanocyte stimulating hormone, and luteinizing hormone releasing hormone in the rat hypothalamus.

Abstract— A 10% homogenate of male rat hypothalami, prepared in 0.32M‐sucrose‐10μM‐CaCl2, was diluted either with one volume of 0.32M‐sucrose‐10μM‐CaCl2 (iso‐osmotic) or with 10μM‐CaCl2 (hypo‐osmotic). A 900 g supernatant fluid fraction (0.9 K‐S) was prepared from the diluted homogenates and fractionated on continuous sucrose density gradients under non‐equilibrium and equilibrium conditions. In the iso‐osmotic 0.9 K‐S thyrotropin releasing hormone (TRH), α‐melanocyte stimulating hormone (α‐MSH), and luteinizing hormone releasing hormone (LHRH) were each found to be sequestered in two populations of particles which were different in size but similar in density. In the hypo‐osmotic 0.9 K‐S, TRH, α‐MSH, and LHRH were each found to be sequestered in a single population of particles. In their sedimentation properties (as judged by differential, non‐equilibrium, and equilibrium density centrifugations), the hypo‐osmotically resistant particles and the small particles present in the iso‐osmotic 0.9 K‐S were identical. However, in their peptide content, the two sets of particles differed from each other. If the total quantity of particle‐bound peptides recovered after gradient centrifugation of the iso‐osmotic 0.9 K‐S is taken as 100%, one finds that the amount of TRH, α‐MSH. and LHRH recovered in the small particles is 39%, 50%, and 39%. respectively, whereas the amount of TRH, a‐MSH, and LHRH recovered in the hypo‐osmotically resistant particles is 42%, 68%, and 67%, respectively. This increase in the quantity of peptides sequestered in the small particles occurred concomitantly with the disappearance of peptides from the large synaptosome‐like particles. It is estimated that within the large synaptosome‐like particles 7% of the TRH, 35% of the a‐MSH, and 45% of the LHRH are associated with hypo‐osmotically resistant particles. Ultrastructural analysis of purified hypo‐osmotically resistant particles containing TRH. α‐MSH. or LHRH revealed a predominance of membrane‐bounded packets of electron‐dense material.