Plasma lipids and chemical, electrophoretic and electron microscopic properties of VLDL, LDL and HDL are examined in rabbits fed a control diet (group I) or diets containing 1% cholesterol (group II), 1% cholesterol + 5% coconut oil (group III) or 1% cholesterol + 5% corn oil (group IV). The diets II, III and IV resulted in hypercholesterolemia, hypertriglyceridemia and hyperphospholipidemia. The lipid-protein composition of VLDL, LDL and HDL is changed by these diets. There is marked increase in the total cholesterol content of all lipoprotein fractions of the high fat dietary groups II, III and IV. The electrophoretic mobilities of the VLDL and LDL II and III are reduced while the respective mobilities in the corn oil group IV are nearly "normal". In contrast to the control LDL fraction I which is not precipitated by heparin, the LDL fractions of the dietary groups II, III and IV are readily precipitated. The apoprotein pattern of the lipoproteins in polyacrylamide gel differs distinctly between the dietary groups, most bands appearing in group IV. An abnormal stacking of lipoprotein particles in electron micrographs of VLDL, LDL and HDL of groups II and III can be observed. In contrast, these lipoprotein fractions of rabbits of the corn oil group IV have morphological properties that are similar to those of the lipoproteins of the control group. It is suggested that these findings are related to the marked reduction of atherosclerosis in rabbits fed a diet with polyunsaturated fat as compared with rabbits on cholesterol and cholesterol-coconut oil diets.

Alanine Transaminase↗

PubMedDate not supplied

Tryptic fragmentation of the calcium transport system in the sarcoplasmic reticulum.

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Adenosine Triphosphatases↗

PubMedDate not supplied

The location of the calcium precipitating protein in the sarcoplasmic membrane.

Fluram, a fast reacting reagent for primary amino groups does not label proteins enclosed in reconstituted sarcoplasmic vesicles (SR vesicles) when applied at low reagent/protein ratios. Hence, Fluram does not penetrate through SR membranes under these conditions. Likewise, the membrane of erythrocytes prevent the reagent from reacting with hemoglobin. However, at high reagent/protein ratios the membranes of the SR vesicles disintegrate. In contrast, liposomal membranes prepared from SR lipids are not affected even at a high degree of labeling. Disintegration of SR membranes starts to occur when the phosphatidylethanolamine fraction is completely substituted by Fluram and the transport protein is labeled with 3-4 mol of Fluram per 100000 d. When closed SR vesicles are labeled at low Fluram/protein ratios, the calcium precipitating protein is four times more intensely labeled than the transport protein. The labeling of the calcium transport protein in closed vesicles excludes its location in the intravesicular space. In SR vesicles solubilized with deoxycholate the relative degree of labeling of the calcium precipitating protein remains unchanged while the transport ATPase is more intensely labeled at the expense of the labeling of the amino lipids. The relative degree of labeling of the protein components depends not only on the number of labable groups but also on the rates with which these groups react with Fluram. Therefore, the experimental data do not give quantitative information concerning the distribution of the protein components in the SR membranes.

Adenosine Triphosphatases↗

PubMedDate not supplied

Effect of lipid modification on fusion of sarcoplasmic reticulum vesicles.

Freeze fracture technique ascertains that sarcoplasmic reticulum vesicles fuse during anisodiametric dehydration which leads to the formation of sheetlike structure of a mean extension of 5000 A. Modification of the membrane lipids by phospholipase A2 digestion or the incorporation of deoxycholate facilitates the coalescence of the vesicles, while it is completely prevented by lipid removal. Membrane fusion during anisodiametric dehydration is considered as resulting from the close contact of highly curved edges from which the membrane proteins have been excluded.

Animals↗

PubMedDate not supplied

A conformational transition of the sarcoplasmic reticulum calcium transport ATPase induced by vanadate.

Vanadate binding to sarcoplasmic reticulum vesicles results in the loss of the externally located high affinity calcium binding sites of the calcium transport ATPase. Conversely the occupation by calcium of the internally located low affinity sites in the vanadate enzyme complex leads to the release of vanadate. Since the total number of calcium binding sites is not diminished by vanadate binding but slightly increases we conclude that vanadate binding induces a transition of the enzymes external high to internal low affinity calcium binding sites. The transposition of external to internal calcium binding sites is accompanied by a definite change in the structure of the sarcoplasmic reticulum membranes. On vanadate binding the asymmetrically arranged electron dense protein particles become symmetrically distributed.

Animals↗

PubMedDate not supplied

Thyroxine induced transformation in sarcoplasmic reticulum of rabbit soleus and psoas muscles.

The properties of the sarcoplasmic reticulum membranes isolated from slow-twitch type I soleus and fast-twitch type II psoas muscles of control and thyroxine treated rabbits were comparatively studied. Membrane yield, maximal calcium storing capacity, ATP-supported calcium uptake, calcium-dependent ATPase activity and calcium-dependent phosphoprotein formation were found to be 3-10 fold higher in psoas than in soleus preparations. Membrane yield, calcium-dependent ATPase activity, ATP-supported calcium transport and calcium-dependent phosphoprotein are at least twice enhanced in the membranes from soleus muscles of animals treated for 14-21 days with thyroxine. The corresponding capacities of the membranes from psoas muscles are not further augmented by the same thyroxine treatment. The maximal calcium storing capacity of the psoas membranes is their sole specific property which is significantly increased. The changes in the properties of the soleus muscles' sarcoplasmic reticulum membranes are engendered by an increase from 5 to 30-50% in the number of type II fibres. Since the calcium transporting properties of the sarcoplasmic reticulum membranes from type II fibres qualitatively differ from those of type I fibres, thyroxine does not only affect quantitative but also qualitative parameters of the muscles' sarcoplasmic reticulum membrane system.

Adenosine Triphosphatases↗

PubMedDate not supplied

The modulation of the calcium transport by skeletal muscle sarcoplasmic reticulum in the hibernating European hamster.

Calcium transport of skeletal muscle sarcoplasmic reticulum was comparatively studied in hibernating and summer active European hamsters (Cricetus cricetus L.). Crude homogenates from psoas, soleus and mixed skeletal muscles were used. Protein yield was strongly reduced in the muscle homogenates of hibernating hamsters. The calcium concentration in the muscle of hibernating hamsters was increased to a much higher content than in the serum. In the same animals the maximal rate of calcium uptake and the calcium storing capacity of sarcoplasmic reticulum were augmented by 43% and respectively 17%. Kinetic experiments with various concentrations of free calcium revealed in the hibernating animals higher uptake rates and a lower apparent calcium affinity than in the summer active hamsters. Some shift of calcium uptake rate and calcium affinity similar to that of a fast-twitch muscle was also observed in winter active animals kept at 22 degrees C under natural photoperiod. By contrast, the activity of the calcium dependent ATPase was not increased, suggesting a tighter coupling during hibernation between calcium dependent ATP-hydrolysis and calcium transport. No seasonal difference was observed in the calcium release by KCl-caffeine from calcium loaded vesicles of sarcoplasmic reticulum. Proportion and size of fibre types were studied with cold cross sections from psoas and soleus muscles. An average atrophy of about 25% was found during hibernation in both muscles. Cytochemistry revealed, however, a different reduction of cross area between type-I- and type-II-fibres, which reaches values up to 46% in the type-II-fast-fibres of the slow soleus muscle. Electron microscopy did not show any definite change in the distribution and amount of sarcoplasmic reticulum. The results suggest that during hibernation a modulation in the properties of calcium transport ATPase of sarcoplasmic reticulum occurs to better support the calcium transport function at low temperatures, which in turn warrants the restoration of ion homeostasis in the course of the arousal.

Adenosine Triphosphatases↗

PubMedDate not supplied

Micromorphometric evaluation of changes in symmetry of sarcoplasmic reticulum membranes induced by vanadate.

Electron micrographs of light sarcoplasmic vesicles fixed with glutaraldehyde and osmium tetroxide followed by contrasting with uranyl acetate and lead citrate have been evaluated by registering their membrane profiles with a microdensitometer. The asymmetric arrangement of the two layers of the vesicular membrane could be ascertained by demonstrating a ratio of 1.5 for the thickness of the outer versus the inner membrane layer which is in general agreement with the proposed protein structure of the calcium transport enzyme. Treatment of the vesicles with low concentrations of vanadate (0.1 mM) results in a significant lowering of the symmetry ratio by 20% by reducing mainly the thickness of the outer membrane leaflet. Removal of the membrane lipids by treating the vesicles with phospholipase A2 and bovine serum albumin diminishes the membrane surface by 50% resulting in a significant increase of both the membrane thickness and the asymmetry ratio by 30 and 12% respectively. The vanadate induced reduction of membrane asymmetry is accentuated after delipidation indicating that the membrane lipids are not essential for the asymmetric appearance of the native membrane. The stability of the spherical form of the vesicles to delipidation implies that the transport molecules are conically shaped allowing strong mutual interactions. At a measured height of the molecule of 80 A in the membrane, the vanadate induced change in symmetry would be brought about by compensatory changes of less than 3 A of the outer (35 A) and the inner (25 A) diameter of the cone.

Animals↗