Mechanism of the cation effect in subfractionation of microsomes.
(9/32)
It was previously found that cations introduced into a discontinuous sucrose gradient exert a very pronounced effect on microsomal vesicles, and this principle proved to be effective in microsomal subfractionation. The mechanism of the cation effect was investigated. By using the radioactive isotopes (137)Cs and (85)Sr, it could be calculated that the amount of ions bound to the various subfractions increases their density by 0.14%, thereby enhancing the sedimentation velocity by only approximately 7%. In the presence of Cs(+) the total volume of the microsomal pellet was decreased by approximately 15%. Assuming this change in volume to be due to a contraction of the individual vesicles, a roughly 2(1/2)-fold increase in sedimentation velocity would be expected. It is further demonstrated, on the basis of light scattering and millipore filtration experiments, that monovalent cations cause an extensive aggregation of rough microsomes and a less pronounced aggregation of smooth microsomes. The mean radius of the sedimenting particles of rough microsomes was found to be at least doubled or trebled in the presence of Cs(+), which would give a 4- to 9-fold increase in the sedimentation velocity. Aggregation, therefore, appears to be the main factor in the accelerated sedimentation of rough microsomes in the presence of CsCl. Divalent cations exert a similar effect on a subfraction of the smooth microsomes. Isolated smooth microsomes are very unstable and often exhibit spontaneous aggregation. The presence of attached ribosomes, however, appears to impart greater stability to the rough microsomes as well as increasing their ability to bind monovalent cations. The primary cause of the aggregation of microsomal vesicles is probably due to a change in net charge. (+info)
Rescue of rous sarcoma virus from rous sarcoma virus-transformed mammalian cells.
(10/32)
Rat cells transformed by the B77 strain of avian sarcoma virus produce no virus-like particles, yet B77 virus was rescued from these cells by Sendai virus-mediated fusion with chicken cells. This virus rescue was not affected by treatment of the chicken cells with agents that rendered the cells incapable of dividing, although such treatment greatly reduced the ability of the chicken cells to plate as infectious centers after infection with B77 virus. Fusion of R(B77) cells with chicken erythrocytes also led to virus rescue, although with less efficiency than fusion with chicken fibroblasts. Therefore, virus rescue was probably due to a factor or factors contributed by chicken cells which aid in virus production. (+info)
Plasmids of Shigella dysenteriae Y6R: a defective Col factor.
(11/32)
The six plasmids of Shigella dysenteriae Y6R were separated by sucrose gradients into five fractions containing deoxyribonucleic acid (DNA), having contour lengths (expressed in units equal to the fraction of the length of the replicative form of phiX174), respectively, of 0.29, 0.35, 0.74, 1.08, and a mixture of 5.7 and 7.2. DNA-DNA hybridization on nitrocellulose filters between each of the plasmids and between plasmid-free S. dysenteriae Y6R host DNA and plasmids was investigated. There was a high degree of homology between the 0.29- and 0.35-unit plasmids. No significant homology was found between any of the other pairs of plasmids. Homologous DNA to the extent of 2.4 copies of the 1.08-unit plasmid was found in the host genome. Homology between the other plasmids and the host genome is very slight, but appears to be significant. About 0.7 of the 1.08-unit plasmid is homologous to the ColE1 factor of Escherichia coli JC411 (ColE1). This plasmid may be defective ColE1 factor with the immunity function intact, but with a defect in the gene leading to the production of active colicin. Electron microscope examination of heteroduplexes formed between the two smallest plasmids and between the 1.08-unit plasmid and the ColE1 factor yielded independent determinations of the extent of homology in agreement with the values determined by hybridization. In the latter case, two nonhomologous regions of substitution of DNA were detected. (+info)
Intrahepatic distribution of portal and hepatic arterial blood flows in anaesthetized cats and dogs and the effects of portal occlusion, raised venous pressure and histamine.
(12/32)
1. Radioactive microspheres were used to determine the distribution of arterial and portal flows within the liver. (141)Ce-microspheres and (51)Cr-spheres were given to allow two determinations of flow distribution in each animal and experiments are described to establish the accuracy and validity of the method.2. Mean flow/g to any lobe or segment of a lobe in a group of animals was not markedly different from the mean flow/g to the whole liver, and in general the liver was homogeneously perfused with both portal and arterial blood. However, in any one liver, some areas received a relatively greater flow (up to 300%) and some a relatively smaller flow (down to 50%) at the time the microspheres were given. The gall bladder received a much smaller portal flow/g than the parenchyma but its arterial flow/g varied widely in different animals.3. If portal flow to an area of parenchyma was reduced by occlusion of a branch of the portal vein, this area received a significantly increased arterial flow.4. An increase in hepatic venous pressure did not cause a significant change in the intrahepatic distribution of either arterial or portal flows in cats.5. In dogs, infusions of histamine into the portal vein caused a redistribution of portal flow away from the free ends of the lobes towards the hilar ends but the distribution between lobes did not change and there was no redistribution of arterial flow. (+info)
Comparison of the effects of hepatic nerve stimulation on arterial flow, distribution of arterial and portal flows and blood content in the livers of anaesthetized cats and dogs.
(13/32)
1. The responses to hepatic nerve stimulation were studied in cats and dogs anaesthetized with sodium pentobarbitone. In three series of experiments, hepatic arterial flow was recorded by an electromagnetic flowmeter, intrahepatic distributions of arterial and portal flows were studied by radioactive microspheres, and hepatic volume responses were measured by a plethysmographic method.2. In cats, nerve stimulation produced a frequency-dependent decrease in hepatic arterial flow which was not maintained and autoregulatory escape occurred. In dogs, the initial decrease in arterial flow was similar but escape did not occur and the vasoconstriction was well maintained.3. In both cats and dogs, stimulation of the hepatic nerves did not cause a redistribution of either arterial or portal flows within the liver. Autoregulatory escape in the liver of the cat was not associated with an intrahepatic redistribution of arterial flow and is best interpreted as relaxation of the same vessels which were initially constricted, due to increased production of a vasodilator factor.4. Stimulation of the hepatic nerves caused a marked frequency-dependent decrease in hepatic volume which was well maintained and the responses were similar in cats and dogs. The quantitative importance of the liver as a blood reservoir is compared in relation to other vascular beds and the concept of the blood volume reserve is discussed. (+info)
Maturation of glomerular blood flow distribution in the new-born dog.
(14/32)
1. Glomerular blood flow distribution was studied in seventy-eight new-born mongrel dogs aged 1-40 days by measuring the distribution of radioactive labelled microspheres within the kidney.2. The microsphere technique was found to be a valid indicator of glomerular blood flow distribution for the new-born dog since (a) the spheres were completely extracted by the kidney, (b) more than 95% of the spheres were trapped in glomerular capillaries, (c) the spheres were evenly distributed within any specific region of the kidney and, (d) the spheres did not interfere with renal haemodynamics.3. Plasma flow per gram tissue to inner cortical glomeruli, relative to that to outer cortical glomeruli, the IC/OC flow ratio, was high at birth, decreased over the first 2 weeks of life and remained relatively constant thereafter. Plasma flow per gram tissue to the outer cortex increased over the whole 40 day period while that to the inner cortex decreased slightly and then increased after 2 weeks.4. The IC/OC flow ratio decreased in a curvilinear fashion as blood pressure rose with maturation. Acute increases or decreases in blood pressure in any animal produced decreases or increases, respectively, in the IC/OC flow ratio.5. There was no correlation between the IC/OC flow ratio and renal extraction of p-amino-hippurate (E(PAH)).6. There was histological evidence that glomerular differentiation persists for 2 weeks during the post-natal period in the dog. This continuing post-natal glomerulogenesis takes place only in the outer cortex.7. These results are consistent with the hypothesis that an important factor in renal maturation is a redistribution of blood flow within the kidney. As the animal matures a greater fraction of the total glomerular blood flow goes to outer cortical glomeruli. This is due partly to the continuing glomerular differentiation taking place in the outer cortical region and partly to the increasing arterial blood pressure occurring with maturation. (+info)
Lymphocyte transformation induced by autologous cells. II. Stimulation by mitogen-induced lymphoblasts.
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Lymphocytes incubated with phytohemagglutinin or concanavalin A develop the capacity to stimulate autologous lymphocyte transformation. This is not attributable to residual mitogen contaminating the lymphoblastic cell preparation as: (a) the dissociation of mitogen from the lymphoblastic cell preparation increases the degree of stimulation observed and (b) the kinetics of lymphocyte transformation stimulated by phytohemagglutinin-induced lymphoblasts is different from that stimulated by phytohemagglutinin. The appearance of the stimulatory determinants on lymphocytes exposed to phytohemagglutinin precedes morphological transformation. (+info)
The effect of salt adaptation on the permeability and cation selectivity of the goldfish intestinal epithelium.
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1. The short-term uptake of Na by the goldfish mucosa was compared using both inulin and choline as markers of extracellular space. The results were virtually identical, the distribution of both choline and inulin increasing rapidly to measure a space at 1 min which then remained nearly constant during a following 4 min incubation.2. Using inulin as space marker, the uptake of various alkali metal cations was determined from a 1 min contact with the mucosa. The relative rates of uptake were Tl > K > Rb > Cs > Na > Li, with a low selectivity ratio, the range of permeabilities being no greater than 5.3. The selectivity sequence was the same in both salt and fresh-water adapted fish. Of the alkali metal cations tested, only Na showed a significantly decreased uptake on adaptation to salt.4. Isolated intestinal preparations from salt-adapted fish showed a reduced short-circuit current compared with fish adapted to fresh water, the values being 12.3 +/- 1.2 and 35.7 +/- 1.5 muA cm(-2) respectively. In both cases the short-circuit current was equivalent to the net transport of Na measured isotopically.5. In Krebs-Henseleit medium, the measured tissue resistance was approximately 100 Omega cm(-2) for both salt and fresh-water adapted fish.6. It is concluded that regulation of cation transport in goldfish intestinal epithelium is specific for Na and mediated primarily through cellular rather than extracellular pathways. (+info)