Ability of insulin to increase calcium binding by adipocyte plasma membranes

Calcium specifically binds to adipocyte plasma membranes, demonstrating two classes of binding sites having affinity constants of 4.5 x 10(4) M-1 and 2.0 x 10(3) M-1. Insulin (100 microunits/ml) added directly to the isolated plasma membranes caused no alteration in calcium binding, whereas incubation of the adipocytes with 100 microunits/ml of insulin resulted in a 2.50 +/- 1.6% increase in calcium binding to the subsequently isolated plasma membranes. The increase in calcium binding produced by insulin resulted from an increase in the maximum binding capacities of both classes of binding sites without alteration in their affinity constants. Additionally, a second pool of calcium in adipocyte plasma membranes has been identified by atomic absorption analysis; it was more than two times larger than the maximum binding capacity of the calcium binding system. This pool of calcium was stable, did not participate in the 45Ca2+ exchange, and was unaltered by insulin treatment. A simialr stable pool of magnesium exists in plasma membranes and was also unaffected by insulin treatment. The increased capacity of the isolated plasma membranes to bind calcium after insulin treatment of the cells may represent an important bioregulating mechanism and supports the concept that calcium may play an important role in the effector system for insulin.

Human fat cell sizing--a quick, simple method

Two methods were used to determine the mean cell diameters of 37 samples of human adipose tissue, obtained by open or needle biopsy. Method I was the sizing of cells in cell suspensions and Method II was a quick, simple method of sizing cells from fixed sections. The agreement between the two methods was good (r = 0.93, P = less than 0.001). The results using Method II were slightly lower than those using Method I, and a correction factor is suggested. Method II has several advantages over Method I and we propose that it is a suitable method for sizing cells when a quick method with a permanent record is required.

Cytochemical localization of catalase and peroxidase in sinusoidal cells of rat liver

The cytochemical localization of catalase and peroxidase in various sinusoidal cells of rat liver, i.e., in Kupffer cells, endothelial cells, and fat-storing cells has been investigated. The alkaline 3,3'-diaminobenzidine technique reveals distinct "catalase-positive particles" in all three cell types. The particles are round to oval-shaped, measuring 0.1 to 0.3 mum. in diameter. The diaminobenzidine reaction product is distributed uniformly over their matrix, often obscuring the distinct limiting membrane. In fat-storing cells the particles appear in close proximity of lipid droplets. No evidence of fusion of the limiting membrane of the particles with that of phagolysosomes containing latex particles was observed. The "catalase-positive particles" appeared often in close proximity of endoplasmic reticulum, but by examining consecutive serial sections we could not find any convincing evidence of direct continuity between the two organelles. In addition to catalase there is an endogenous peroxidase in the endoplasmic reticulum and nuclear envelope of Kupffer cells. Whereas peroxidase is sensitive to aldehyde fixation and has its optimal pH in the neutral range, the staining for catalase requires prior fixation with glutaraldehyde and isoptimal at pH 10.5. By using proper fixation and incubation conditions the two enzymes have been visualized selectively, and it is demonstrated that they occupy two distinct intracellular compartments within the Kupffer cells: the catalase in the matrix of particles and the peroxidase in the endoplasmic reticulum. The possible functional role of catalase in various sinusoidal cells is briefly discussed.

Capillary lengths and areas, and intercapillary distances in tissue near the human knee

Quantiative stereological electron microscopy has been used to investigate the capillary lengths, surface areas and intercapillary distances in the tissues around the human knee, the synovial membrane, synovial capsule, fat and tendon. The vascularity of these regions was much less than in other areas of the body, especially muscle.

Ultrastructural observations on differentiating human preadipocytes cultured in vitro

A cell type, preadipocytes, isolated from the stroma of adult human adipose tissue appears capable of differentiating, in culture, into a cell with morphological features similar to that observed in terminally differentiated human adipocytes cultured under similar conditions. During this process of differentiation, preadipocytes develop extensive rough endoplasmic reticulum with prominent cisternae, the chromatin of most nuclei becomes decondensed and lipid bodies accumulate to levels observed in cultured adipocytes. Fibroblasts derived from non-adipose tissue do not undergo the same morphological changes when cultured under similar conditions.

Cell remodeling in the fat body of an insect

The fat body of the Lepidopteran, Calpodes ethlius, undergoes major functional changes during larval-adult metamorphosis. These changes occur in conjunction with extensive cell remodeling - a process whereby one population of cellular organelles is destroyed and replaced by another during development. Fat body organelles including mitochondria, microbodies, and RER are destroyed on a massive scale shortly before pupation (Locke and Collins, 1965; Locke and McMahon, 1971) a new populations of each are regenerated shortly after emergence of the adult. In addition, protein, lipid and RNA reserves formed shortly before pupation and multivesicular bodies formed shortly before emergence are secreted into the haemocoel during the first few days of adult life. Electron microscopic studies using tracer techniques, cytochemical and enzyme localization procedures, and sterological analyses have been undertaken to determine the time course and mechanism of organelle regeneration and the fate of reserves stored in the fat body.

Ultrastructural development of bone marrow adipose cell

The postnatal development of bone marrow adipose cells was studied by sequential examination of marrow tissue obtained from the tibia and femur of 1- to 8-week-old rabbits. The bone marrow adipocyte begins to develop 2 weeks after birth. Its cellular origin differs from the "fibroblast-like" cell that is the progenitor of the extramedullary adipocyte. The marrow pre-adipocyte is associated with the sinus endothelium and adventitial cells, but is not associated with collagen and does not contain abundant organized rough endoplasmic reticulum. Unlike the extramedullary adipocyte, the course of differentiation of the medullary adipocyte is not characterized by the appearance of glycogen; furthermore, during the coalescence of lipid droplets to form larger fat globules, cytoplasmic organelles, such as mitochondria and ribosomes, are trapped within the lipid substance to form intralipid vacuoles containing degraded cytoplasmic organelles. The possible significance of these morphologic differences between the developing bone marrow adipocyte and that of its extramedullary counterpart is discussed.

Influence of age on size and number of fat cells in the epididymal depot

The extensive literature on the effect of rat age on the size and number of adipocytes in adipose tissue depots relates solely to young developing rats and young adults. Therefore a study was carried out in our laboratory on the cellular characteristics of the epididymal depot of the Fisher 344 strain of rats through virtually the entire life-span. Collagenase digests of this depot prepared from rats of 9, 13, 26, 52, 104, and 130 wk of age yield a population of cells with diameters greater than 30 mum identified as adipocytes or "fat cells." A remarkably complex pattern of changes in both the size and the number of these fat cells in the epididymal depot occurred through the life-span of the rats. The epididymal depots also contain some cells with diameters around 10 mum which have a morphology similar to that of the classic adipocytes; such cells may be preadipocytes.

On the ultrastructure of hibernoma

An electron-microscopic study of hibernoma and a review of the histogenesis, development, and post-natal structural composition of brown and white adipose tissue are presented. The ultrastructural features of hibernoma include multivacuolated and univacuolated cells containing variable numbers of lipid vacuoles, abundant moderately pleomorphic mitochondria with transverse cristae, lysosomes, lipofuscin granules, pinocytotic vesicles, well-formed basal lamina, and prominent subplasmalemmal condensations. The latter have not been previously reported in hibernoma, brown adipose tissue or white adipose tissue, although gap junctions have been observed in brown adipose tissue of newborn mice. It is concluded that the ultrastructural observations support the concept proposed decades ago that hibernoma represents the neoplastic counterpart of brown adipose tissue.

Comparison of plasma membranes and endoplasmic reticulum fractions obtained from whole white adipose tissue and isolated adipocytes

The influence of the mode of preparation upon some of the characteristics of white adipose tissue plasma membranes and microsomes has been reported. Plasma membrane fractions prepared from mitochondrial pellet were shown to have higher specific activities of (Mg2+ + Na+ + K+)-ATPase than plasma membranes originating in crude microsomes. Isolation of fat cells by collagenase treatment was found to result in a decrease in specific activity of the plasma membrane enzymes; in plasma membranes prepared from isolated fat cells, the specific activity values obtained for (Mg2+ + Na+ +k+)-ATPase and 5'-nucleotidase were only 42% and 6.3% respectively of those obtained in plasma membranes prepared from whole adipose tissue. Purification of whole adipose tissue crude microsomes by hypotonic treatment caused extensive solubilization of the endoplasmic reticulum marker enzymes, NADH oxidase and NADPH cytochrome c reductase. The lability of endoplasmic reticulum marker enzymes, however, was found to be greatly diminished in the preparations from isolated fat cells. The possibility that NADH oxidase and NADPH cytochrome c reductase activities found in the plasma membranes are microsomal enzymes adsorbed by the plasma membranes is discussed. The peptide patterns as well as the NADH oxidase and NADPH cytochrome c reductase activity patterns of plasma membranes and purified microsomes were compared by means of sodium dodecyl sulfate or Triton X-100 polyacrylamide gel electrophoresis.

Stimulation of epinephrine-sensitive fat cell adenylate cyclase by cytosol: effect of cholera toxin

Cytosol prepared from rat epididymal fat cells by centrifugation at 100,000 X g for 1 hr was found to enhance the basal and epinephrine-sensitive adenylate cyclase [EC 4.6.1.1; ATP pyrophosphate-lyase (cyclizing)] of fat cell ghosts. Cholera toxin also stimulated adenylate cyclase and increased the response to epinephrine in fat cells. A possible relationship between the adenylate cyclase modifying activities of cytosol and the effects of cholera toxin was sought. Cytosol from freshly prepared fat cells added to ghosts prepared from cells that had been exposed to toxin for varying periods showed a progressive loss of responsiveness to cytosol epinephrine-enhancing activity. The effect appeared within 15 min after toxin exposure, a full 30 min before any direct effect of toxin on adenylate cyclase was seen. Since exposure to toxin decreased membrane response to cytosol epinephrine-enhancing activity, the possibility that epinephrine-enhancing activity in cytosol might be altered by toxin was explored. Cytosol from cells exposed to toxin for varying periods lost epinephrine-enhancing activity to an appreciable degree within 15 min. Examination of these early events after exposure to toxin should clarify the way in which this bacterial substance affects mammalian cells. The cytosol epinephrine-enhancing activity was destroyed by boiling for 3 min and was partially inactivated by trypsin. It was nondialyzable and stable at -70 degrees.

Mechanism of activation of adenylate cyclase by cholera toxin

Cholera toxin (choleragen) can stimulate adenylate cyclase [EC 4.6.1.1; ATP pyrophosphate-lyase (cyclizing)] activity in whole particulate fractions or purified plasma membranes of homogenates of isolated fat cells provided special precautions are taken to stabilize the enzyme during the required preincubation period. As observed with intact cells, the activation exhibits a protracted (about 25 min) lag phase, and it is blocked by ganglioside GM1 and choleragenoid ("binding" subunit of toxin). The 36,000 molecular weight subunit ("active" subunit), a hydrophobic polypeptide which does not block choleragen binding or action, can directly activate the enzyme in intact cells without a lag phase. Its effects are not blocked by ganglioside GM1 or choleragenoid, yet the stimulated activity exhibits reduced fluoride and enhanced isoproterenol sensitivity, properties characteristic of the choleragen-activated enzyme. Binding of the 125I-labeled 36,000 molecular weight subunit to cells is not saturable and is unaffected by gangliosides, choleragen, or choleragenoid, and the bound material behaves as an integral membrane protein; this protein may simply partition into the membrane matrix. With increasing time of incubation cell-bound choleragen may dissociate into its component subunits, but these remain in the membrane. Using a double antibody immunoprecipitin system, substantial precipitation of cyclase activity occurs with antisera against the 36,000 molecular weight subunit provided toxin activation has occurred. The normal process of activation may involve an initially inactive toxin--ganglioside complex which, as a result of lateral mobility and multivalent binding (lag phase), results in destabilization of the molecule with release of the "active" subunit into the membrane core where it can spontaneously associate with and perturb the cyclase complex.

Ultrastructural localization of insulin receptors on adipocytes

The method for preparing a stable, biologically active, covalently linked ferritin--insulin complex has been modified to provide a 25-fold increase in yield compared to the original procedure while reducing the molar fatio of ferritin to insulin to 1:1 from 40:1. Ultrastructural studies of isolated adipocytes revealed specific binding of ferritin--insulin to the cell surface in irregular clusters associated with the glycocalyx coating. The number of ferritin--insulin molecules observed was consistent with the number of sulin molecules observed was consistent with the number of receptors calculated from 125I-labeled insulin binding studies. The ferritin--insulin was not observed in the cytoplasm of the cell but was found on the convave side of surface connected vesicles. These surface connected vesicles were part of an alveolar-like system of plasma membrane invaginations which project in various directions in the cytoplasm and by thin sectioning can appear as pinocytotic-like microvesicles. The morphological observations on ferritin--insulin binding were supported by the finding that 125I-labeled insulin binding was almost exclusively localized to highly purified plasma membranes isolated by fractionation of adipocytes after incubation with 125I-labeled insulin. These data supported the theory that insulin did not need to enter a cell to cause biological effects and was consistent with the negative cooperativity concept of insulin binding to cell receptors.

Studies of the biological activity of insulin, cyclic nucleotides and concanavalin A in the isolated fat cell

The insulin or proinsulin response of the isolated rat adipocyte was destroyed by preincubation with trypsin. After 120 minutes, biological responsiveness partially regenerated. Similarly, the biological responsiveness of the isolated fat cell to non-suppressible insulin-like activity (NSILA) was only partially destroyed following trypsin digestion, and did not regenerate. In contrast to the above, cyclic AMP or dibutyryl cyclic AMP effects were unaltered by trypsin or neuraminidase digestion.

Ultrastructural study of the neural fat-body system in the cockroach Periplaneta americana

The neural fat-body system of the ventral nerve cord in the cockroach Periplaneta americana was studied with the light and electron microscopes. This adipose tissue surrounds the connectives and extends over the ganglia. The adipose cells typically contain numerous extremely large lipid inclusions, pleomorphic lysosomes, and tightly packed glycogen granules. The neural lamella consists of a thick inner layer rich in collagen fibers and a thin outer layer of granular material. At points where the fat body is attenuated, this granular layer is split and the outer lamina is reflected superficially to ensheath and apparently to anchor the fat body.

Acute hemorrhagic pancreatitis (massive necrosis) with fat necrosis induced in mice by DL-ethionine fed with a choline-deficient diet

Female, albino mice were fed a choline-deficient diet containing 0.5% DL-ethionine. All animals died within 5 days due to the development of an acute hemorrhagic pancreatis with fat necrosis throughout the peritoneal cavity. The apancreatitis was characterized by a massive necrosis of the exocrine parenchyma with intense hemorrhage and inflammatory reaction of the stroma. The sequence of histologic and ultrastructural alterations occurring in the acinar cells of the pancreas were studied in mice fed the diet for 1, 2, and 3 days. Major findings consited of accumulation of zymogen granules, vacuolation due to foci of cytoplasmic degradation, and alterations in the morphology of the zymogen granules. The pancreatitis appears to be due to intraparenchymal activation of zymogens, resulting from a synergistic action of choline deficiency with the basic toxicity of ethionine toward the acinar cells of the pancreas. The experimental model simulates closely the acute hemorrhagic pancreatitis with fat necrosis occurring in humans and may prove useful for exploring the pathogenesis of this condition.