Light and electron microscopic detection of anionic sites in the rat choroid plexus

Electron microscopy of ultrathin sections stained with cationic iron colloid revealed that, in the choroid plexus of the rat brain ventricles, the luminal surface and fenestral diaphragm of the capillary endothelium as well as the basement membranes of the endothelium and epithelium are strongly anionic or intensely negatively charged. The iron colloid reaction to these anionic sites was erased by treatment with hyaluronidase or digestions with chondroitinase ABC/heparitinase/keratanase. These results indicate that sulfated proteoglycans provide such anionic sites of the choroidal capillaries. Discussion suggested that the negative charge on the luminal surface of the capillary endothelium prevents the adhesion of blood cells to capillary walls and also prevents endothelial adhesion by their repelling each other. It was further discussed that the negatively charged endothelial fenestrae and basement membranes may act as a charge barrier to inhibit the passage of anionic molecules.

Expression, structure and chromosomal localization of the human cGMP-binding cGMP-specific phosphodiesterase PDE5A gene

cGMP-binding, cGMP-specific phosphodiesterase which is encoded by the PDE5A gene plays important roles in cardiovascular system, and is a significant target molecule of therapeutic agents. However, little is known about molecular characteristics of the human PDE5A gene. The 4.4-kb cDNA encoding human PDE5A was isolated from lung and placenta cDNA libraries. The deduced amino acid sequence analysis demonstrated that N-terminal amino acid sequence is dissimilar to that of rat PDE5A [Kotera, J., Yanaka, N., Fujishige, K., Imai, Y., Akatsuka, H., Ishizuka, T., Kawashima, K. & Omori, K. (1997) Eur. J. Biochem. 249, 434-442]. Human PDE5A mRNA is produced in high amounts in various tissues such as pancreas, skeletal muscle, placenta, heart, thyroid, adrenal cortex, testis, small intestine and stomach. In addition, the megakaryocyte-like cell line Dami cells and two types of human vascular smooth muscle cells also produce the mRNA. Over 100-kb chromosomal DNA corresponding to the human PDE5A gene was isolated and analyzed. The human PDE5A gene was revealed to contain 21 exons. Comparison of genomic organization with the rod photoreceptor phosphodiesterase beta-subunit gene (PDE6B), which is another kind of cGMP-specific phosphodiesterase, has shown that the PDE5A and PDE6B genes are very similar in their relative exon intron organization. In particular, the evolutionary relatedness of these genes was suggested in the catalytic domain. Furthermore, chromosomal location of the PDE5A gene was defined as being chromosome 4q26 by fluorescent in situ hybridization analysis.

Localization of a serine proteinase inhibitor, B-43, in the bovine pancreas

B-43, a serine proteinase inhibitor belonging to the ovalbumin branch of the serpin superfamily, was purified and cloned from bovine brain. Since [35S]-labeled B-43 forms SDS-stable complexes with pancreatic serine proteinases, trypsin, alpha-chymotrypsin, and kallikrein, it has been suggested that B-43 is capable of inhibiting these serine proteinases and that B-43 may be present in the pancreas. In the present study, we investigated the localization of B-43 in the bovine pancreas immunohistochemically and examined the effect of B-43 on the amidolytic activities of pancreatic serine proteinases. Strong B-43-like immunoreactivity was localized in acinar cells, especially in the basal sides of the cells where the rough endoplasmic reticulum is located. The nuclei of the subpopulation of acinar cells were also immunoreactive for B-43. The recombinant glutathione S-transferase-B-43 fusion protein inhibited the amidolytic activity of trypsin and, to a lesser extent, alpha-chymotrypsin and kallikrein, but not elastase. These results suggest a role of B-43 in regulating serine proteinases both in the cytoplasm and the nucleus.

Evaluation of disk capture with a splint repositioning appliance: clinical and critical assessment with MR imaging

OBJECTIVE

The purpose of this study was to evaluate disk repositioning clinically and through use of magnetic resonance imaging after the insertion of a disk repositioning appliance.

STUDY DESIGN

Seventy-four patients with 82 temporomandibular joints showing middle to late opening movement click and closing movement click near maximum intercuspation were treated with a mandibular full-coverage repositioning splint. These joints were assessed clinically and by means of magnetic resonance imaging for disk recapture.

RESULTS

According to clinical assessment, 75.6% (62/82) of the joints were treated successfully; no click was observed from the splinted mandibular position. When compared with the results of magnetic resonance imaging assessment, clinical assessment showed an accuracy rate of 91.5%, although the incidence of the false negatives was high (40%).

CONCLUSIONS

The results of this study showed that about 70% of reducing displaced disks were captured with use of the disk repositioning appliance. And it was also suggested that magnetic resonance imaging is helpful to evaluate disk repositioning therapy.

Vitamin E reduces glucocorticoid-induced growth inhibition and lipid peroxidation in rats

This experiment was conducted to study the effects of vitamin E on growth inhibition and lipid peroxidation in rats treated with different levels of corticosterone (CTC). Rats (Sprague-Dawley strain, 5 weeks of age) were divided into two groups: control group receiving a basal diet containing 60 mg DL-alpha-tocopheryl acetate/kg diet, and vitamin E group receiving the same diet supplemented with 5,000 mg tocopherol. After 6 days, rats of both diet groups were further divided into three groups by dose levels of CTC treatment (0, 25, and 100 mg CTC/kg body weight/d). CTC was administered to the rats by subcutaneous injection for 4 d. Growth was dose-dependently inhibited by the CTC treatment. Feeding the vitamin E diet significantly (p < 0.05) improved growth retardation. Feed efficiency was lowered by CTC treatment, while this was significantly (p < 0.05) minimized by feeding the vitamin E diet. Lipid peroxidation (TBARS) in the liver was elevated by the CTC treatment (p < 0.001) when the rats were fed the basal diet. The increment in TBARS was significantly (p < 0.001) reduced by vitamin E. The activities of glutathione S-transferase (GST) and superoxide dismutase (SOD) were significantly reduced by the CTC treatment in a dose-dependent manner in both dietary groups. Feeding vitamin E significantly (p < 0.001) improved the reduction in GST activity. The SOD activity showed some tendency. The present results demonstrate the effectiveness of vitamin E in improving growth retardation in glucocorticoid-treated rats and suggest that reductions in increased lipid peroxidation due to CTC may be an important factor of the action of vitamin E.

Mast cells in osteoarthritic and rheumatoid arthritic synovial tissues of the human knee

The distribution and density of mast cells in the normal and diseased synovial membranes were investigated. The mast cell count (MCC) in the osteoarthritic (OA) synovium (36.9 +/- 26.9 cells/mm2) was significantly higher than that in the rheumatoid arthritic (RA) synovium (18 +/- 12.3 cells/mm2). There was a marked positive correlation between the MCC and the volume of joint fluid in OA (r = 0.544). There was a marked negative correlation between the MCC and the volume of joint fluid in RA (r = -0.478). The synovial inflammatory score had a poor correlation with the MCC in OA (r = 0.377) and RA (r = 0.305). No correlation was noted between MCC and age, sex, roentgenographic grades, disease duration, C-reactive protein or leucocyte number in synovial fluid. Our data suggests, thus, that mast cells could be involved in the pathogenesis of inflammatory diseases of the synovium, especially in the mechanism of hydroarthrosis.

Change of position of the temporomandibular joint disk with insertion of a disk-repositioning appliance

OBJECTIVE

We report alteration of the temporomandibular joint disk and the condyle position through the construction of a mandibular full-coverage occlusal appliance (often referred to as a disk repositioning appliance).

STUDY DESIGN

Forty-five joints with displaced disks with reduction were available for the study. We assessed these joints for disk recapture and the change of disk position with insertion of the appliance using magnetic resonance imaging.

RESULTS

Of the 41 joints that had a recaptured disk with insertion of the splint, 25 slid in a posterior direction, although the amount of movement was negligible. No disk slid posteriorly in the joints without splint capture.

CONCLUSIONS

On the basis of our results, we conclude that many of the occasionally displaced disks might have moved backward with successful treatment involving a disk-repositioning splint. However, the amount of the movement was negligible.

Negative charges bound to collagen fibrils in the rabbit articular cartilage: a light and electron microscopic study using cationic colloidal iron

Negative charged sites in the normal rabbit articular cartilage were investigated using cationic colloidal iron methods. In light microscopy of the cartilage stained with the colloidal iron at pH 1.5, a distinct Prussian blue reaction was observed in the pericellular matrix, and a weak blue reaction in the territorial and interterritorial matrices. At pH 7.0, a diffuse Prussian blue reaction was observed in the pericellular and interterritorial matrices. Digestion with chondroitinase ABC, hyaluronidase and keratanase could not erase the Prussian blue reaction. However, the sections digested with collagenase followed by chondroitinase ABC showed significant elimination of the Prussian blue reaction. Electron microscopy of ultrathin sections stained with the colloidal iron at pH 1.5 revealed that the cationic colloid particles were deposited abundantly in the pericellular matrix and dotted along collagen fibrils in the territorial and interterritorial matrices. The present results suggest that negatively charged sites in the articular cartilage derive mostly from chondroitin sulfate, whose proteoglycans firmly bind to collagen fibrils. Such an ultrastructure may maintain the electrostatic microenvironment in the collagen plexus, holding much water in the cartilage matrix, and also producing biomechanical properties such as tensile strength and elasticity of the cartilage.

Perineuronal sulfated proteoglycans and cell surface glycoproteins in the visual cortex of adult and newborn cats

Sections of the visual cortex of newborn (1-4 weeks after birth) and adult cats were stained with cationic iron colloid, aldehyde fuchsin or lectins (lectin Vicia villosa, soybean and Wisteria floribunda agglutinins). Many neurons in the adult cat visual cortex contained perineuronal sulfated proteoglycans detectable with cationic iron colloid and aldehyde fuchsin, or cell surface glycoproteins reactive to lectins. Double staining indicated that some of the lectin-labeled neurons were not stained with cationic iron colloid, and also that some of the cationic iron colloid-stained neurons were not labeled with lectins. The perineuronal sulfated proteoglycans and cell surface glycoproteins developed 3 weeks after birth. In the newborn cats 1-2 weeks after birth, no neurons were reactive to cationic iron colloid, aldehyde fuchsin or lectins. In the newborn cats 3-4 weeks after birth, it was clearly observed that the cytoplasm of the glial cells closely associated with the neurons containing the perineuronal sulfated proteoglycans showed an intense reaction to cationic iron colloid and aldehyde fuchsin, and that the Golgi complexes of the neurons with cell surface glycoproteins were intensely labeled with lectins. These findings suggest that the perineuronal sulfated proteoglycans are derived from the associated glial cells, and that the cell surface glycoproteins are produced by the associated nerve cells.

Growth factors for a primary chick muscle cell culture from shochu distillery by-products

An unidentified growth factor (UGF) was separated from shochu distillery by-products (SDBP) and its effect on the growth of a primary chick muscle cell culture was investigated. Chick muscle cells were isolated from fertile eggs (13-day-old embryos) of commercial broilers. UGF was separated on Sephadex LH-20 with a solvent system of water-methanol-ethylene dichloride (10:90:20, v/v), and the fraction eluted between 136 and 164 min was collected (fraction I). Fraction I was further purified by HPLC with an Inertsil ODS-2 column using a solvent system of methanol-butanol (80:20, v/v). Three fractions having retention times of 3.76, 4.57, and 5.12 min were collected and are referred to as fraction A, B, and C, respectively. In experiment 1, chick muscle cells were cultured in an m-199 medium containing 0.001, 0.01, or 0.1% of fraction I. In experiment 2, chick muscle cells were cultured with 0.01 or 0.005% of each fraction A, B, and C. Creatine kinase (CK) activity, protein and DNA contents were measured as indices of myotube growth, cell growth and cell proliferation, respectively. N tau-methylhistidine (N tau-MH) release from the muscle cell was also measured to observe the effect on proteolysis. In experiment 1, the protein content was significantly (p < 0.05) increased by fraction I, despite the low dose level. CK activity was significantly (p < 0.05) higher than the control when 0.001% of fraction I was added to the medium. However, increasing the level beyond 0.01% did not further increase the CK activity. The DNA content was not significantly changed. In experiment 2, the protein content, CK activity, and DNA content were significantly (p < 0.05) higher when fractions A and B were added to the medium. However, this was not the case when fraction C was added. N tau-MH release was significantly (p < 0.05) higher when fraction A was added, but, was significantly (p < 0.05) lower when fraction B was added, while fraction C had no effect on N tau-MH release. The present results show that SDBP contained two growth-promoting factors for a primary chick muscle cell culture, although their modes of action may be different.

Perineuronal sulfated proteoglycans and cell surface glycoproteins in adult and newborn mouse brains, with special reference to their postnatal developments

Sections of the retrosplenial cortex from adult and newborn mouse brains were observed with a light microscope. The retrosplenial cortex of the adult animals contained many neurons (10% of the total), including some dark neurons, with perineuronal sulfated proteoglycans detectable with cationic iron colloid and aldehyde fuchsin. The retrosplenial cortex of the adult animals also contained many neurons (10% of the total) with cell surface glycoproteins reactive to lectin Vicia villosa, soybean or Wisteria floribunda agglutinin. Double staining showed that the majority (75%) of the neurons labeled with lectins were stained with cationic iron colloid, and that some (25%) of them were not stained with this colloid. Double staining also showed that some (25%) of the neurons stained with cationic iron colloid were not labeled with lectins. These findings indicate that the perineuronal sulfated proteoglycans are, at least partly, independent from the cell surface glycoproteins. Observations of the sections from the newborn animals revealed that the perineuronal sulfated proteoglycans were produced by the associated satellite astrocytes 3-4 weeks after birth, and that the cell surface glycoproteins were produced by the associated nerve cells at earlier stages, or 2-3 weeks after birth. Dark neurons began to appear 3-4 weeks after birth. These dark neurons or their Golgi complexes were also reactive to lectins, suggesting the production of cell surface glycoproteins.

Dark and light neurons in the human brain, with special reference to their reactions to Golgi's silver nitrate, luxol fast blue MBS and azocarmine G

Sections from the human somatosensory cortex were observed with a light microscope. The neurons were classified into light and dark ones. The light neurons were slightly stained with thionin, luxol fast blue MBS and azocarmine G (80% of all neurons). The dark neurons were more or less shrunken, and stained intensely with these dyes (20% of all neurons). Double staining with luxol fast blue MBS and azocarmine G was especially useful to demonstrate the dark neurons, since it clearly stained even their fine processes. Neither light nor dark neurons were reactive to nick end labeling for detection of DNA fragmentation. Triple staining with Golgi's silver nitrate (or Gallyas's ammoniacal silver carbonate), luxol fast blue MBS and azocarmine G show that the majority of the dark neurons were argyrophilic (argyrophilic dark neurons, 15% of all neurons), while some of them were not argyrophilic (non-argyrophilic dark neurons, 5% of all neurons). Triple staining also showed that the light neurons were only occasionally argyrophilic (argyrophilic light neurons, 5% of all neurons); usually, the light neurons were not argyrophilic (non-argyrophilic light neurons, 75% of all neurons). The results confirm that dark neurons usually represent certain populations of neurons in the human brain, and that they are basically identical to the argyrophilic neurons. The discussion suggests that the argyrophilic light and dark neurons are excited cells, the non-argyrophilic dark neurons are exhausted cells, and the non-argyrophilic light neurons are resting cells. Triple staining further demonstrated that some glial cells were darkened and stained with Golgi's silver nitrate or Gallyas's silver carbonate. Additional Golgi's silver block staining showed that the argyrophilic neurons stained by the conventional block staining method usually possessed a shrunken cell body, which was characteristic of the dark neurons.

Localization of membrane-associated sialomucin on the free surface of mesothelial cells of the pleura, pericardium, and peritoneum

Strong anionic sites, as recognized by deposition of cationic colloidal iron even at pH 1.5, were distributed on the free surfaces of the mesothelia of the mouse pleura, pericardium, and peritoneum. Methylation inhibited colloidal iron staining on the surface, and successive saponification restored it. Digestion with neuraminidase or hydrolysis of sialic acid with H2SO4 erased the colloidal iron staining. Lectin Limax flavus agglutinin (LFA), which is specific for sialic acid, labeled the free surface of the mesothelium. All these findings strongly suggested that the surface substance contained sialic acid. Moreover, prior treatment with LFA inhibited the mesothelial surface stain with colloidal iron. In transmission electron microscopy, the colloidal iron (pH 7.3)-stained substance took the shape of fine strands of 50-300 nm in length. These characteristics of the substance on the mesothelial surface correspond well with biochemical properties of membrane-associated sialomucin, whose strong and abundant negative charges produce repulsive forces between facing serosal surfaces. This may contribute to prevent serosal adhesion and to reduce friction during movements of organs.

Blood flow patterns in the rat pancreas: a simulative demonstration by injection replication and scanning electron microscopy

Scanning electron microscopy of vascular casts prepared by arterial injections of intentionally reduced amounts of resin showed that in the rat pancreas, the casting medium fills blood capillaries in the endocrine islets more promptly than those in the exocrine lobules and secretory ducts. Furthermore, the exocrine lobules containing endocrine islets allowed a more rapid resin flow through the insulo-acinar portal route than those lobules lacking an islet. The capillaries of secretory ducts were the last portions to be filled with resin. Since the resin used in this study was as viscous as blood and injected under a physiological pressure, the microcirculatory patterns demonstrated by the present method reflect the physiological flow pattern of blood in the pancreas.

Pancreatic insulo-acinar portal systems in humans, rats, and some other mammals: scanning electron microscopy of vascular casts

Scanning electron microscopy of vascular casts showed that in the mouse, rat, and guinea pig, the pancreatic endocrine islets were frequently interlobular in position and emitted insulo-venous efferent vessels directly draining into veins. In these animals, the intralobular islets, located within the exocrine lobules, issued insulo-acinar portal vessels continuous with the lobular capillaries in addition to the insulo-venous efferent vessels. In humans, monkeys, cows, pigs, dogs, cats, and rabbits, essentially all islets in the pancreas were intralobular in location and emitted the insulo-acinar portal vessels only. In man and animals examined, especially in the murine species, many lobules lacked an islet, therefore the insular control over the exocrine pancreas seemed to be effected in more or less restricted areas of lobules.

Effect of environmental temperature on muscle protein turnover and heat production in tube-fed broiler chickens

The present experiments were undertaken to investigate the effects of environmental temperatures on growth, abdominal fat content, rate of muscle protein turnover, and heat production in tube-fed intact male broiler chickens. Plasma concentrations of thyroxine (T4), triiodothyronine (T3), and corticosterone (CTC) were also examined. Chicks (15 d old) were kept at different environmental temperatures (16, 19, 22, 25, 28, 31, and 34 degrees) and given the experimental diet (200 g crude protein/ kg, 13.57 MJ/kg metabolizable energy) by tube three times daily throughout the 12 d experimental period. In the hot conditions, except for 34 degrees, body-weight gain was significantly higher than in the cold conditions. Thus, food conversion ratios (food:gain ratios) were lower when the birds were exposed to the hot conditions other than 34 degrees. Likewise, abdominal fat content was significantly increased, and heat production was lower in the groups kept under the hot conditions other than 34 degrees. The rate of skeletal muscle protein turnover and plasma concentration of CTC were decreased when the birds were exposed to hot conditions other than 34 degrees, suggesting a role of CTC in the regulation of muscle protein turnover. Plasma concentrations of T4 and T3 were significantly decreased as environmental temperature increased. These results clearly show that plasma concentrations of thyroid hormones and CTC are associated with accelerated muscle protein turnover and heat production.

Perineuronal sulfated proteoglycans, cell surface glycoproteins and dark neurons in the cingulate cortex of newborn and adult rats

Many neurons in the adult rat cingulate cortex possess perineuronal sulfated proteoglycans detectable with cationic iron colloid and aldehyde fuchsin, or cell surface glycoproteins reactive to lectin Vicia villosa or soybean agglutinin. The perineuronal sulfated proteoglycans develop three to four weeks after birth. The cell surface glycoproteins develop at earlier stage or two to three weeks after birth. Dark or active neurons begin to appear three to four weeks after birth. These findings indicate that the brain matures after birth or during weaning period.

Perineuronal sulfated proteoglycans in the adult rat brain: histochemical and electron microscopic studies

Neurons of cerebellar nuclei in the rat brain had a marked surface coat which was stained with cationic iron colloid or aldehyde fuchsin. Neurons with a similar surface coat were also noted in the retrosplenial cortex. The surface coat was stained doubly with cationic iron colloid and aldehyde fuchsin. Digestion with hyaluronidase eliminated the stainability of the surface coat to both agents. Combined digestion with chondroitinase ABC, heparitinase and keratanase eliminated the cationic iron colloid staining but did not interfere with the aldehyde fuchsin staining. Electron microscopy of ultrathin sections revealed that the iron particles were deposited in the perineuronal tissue spaces. These findings indicate that the surface coat consists of sulfated proteoglycans which occupy, as the extracellular matrix, the perineuronal tissue spaces. Many neurons in the retrosplenial cortex were labeled with lectin Vicia villosa agglutinin. Double staining revealed that these lectin-labeled neurons are usually reactive to cationic iron colloid. Few neurons in the cerebellar nuclei were labeled with lectin V. villosa agglutinin.

Rat parathyroid gland, with special reference to its blood vascular bed, pericapillary space and intercellular space

The blood vascular bed, perivascular space and intercellular space of the rat parathyroid gland were studied using scanning electron microscopy of vascular casts, freeze-cracked tissue samples, and NaOH-digested tissue blocks. The findings were supplemented by transmission light and electron microscopy of iron colloid-treated or enzyme-digested tissue sections. The rat parathyroid gland contained a rich network of capillaries. These capillaries were surrounded by marked pericapillary spaces which were demarcated by basal lamina of both capillaries and parenchymal cells. The pericapillary spaces contained numerous collagen fibrils, and issued many crista-like projections which ran deep into the sheets of parenchymal cells. The intercellular spaces of parenchymal cells contained neither basal lamina nor collagen fibrils. The surfaces of the parenchymal cells showed strong negative charging, and maintained the intercellular spaces. The luminal surfaces of the capillary endothelium also showed strong negative charging, and maintained the capillary lumen.

Calcitonin decreases corticosterone-induced skeletal muscle calpain activity

The effects of calcitonin (CT) administration on calcium (Ca) concentrations in plasma and skeletal muscle as well as the calpain activity of skeletal muscle were examined in young growing male rats treated with corticosterone (CTC). The rats received subcutaneous injections of CTC (5 mg/100 g body weight/day), or both CTC and CT (100 m unit/100 g body weight/day) for four days. Control rats received placebos. The rats were sacrificed 24 h after the final injections, and blood was taken followed by dissections to remove gastrocnemius and extensor digitorum longus muscles. Plasma Ca concentration was increased and muscle Ca concentration and its calpain activity tended to be increased by CTC. The CTC-induced increases in muscle Ca concentration and its calpain activity were significantly minimized by the simultaneous injection of CT. However, CTC-induced hypercalcemia was not minimized by CT. The present observations indicate that CT decreases Ca concentration in skeletal muscle cell and its calpain activity, followed by a suppression of muscle proteolysis in rats treated with CTC.

Neurons with perineuronal sulfated proteoglycans in the mouse brain and spinal cord: their distribution and reactions to lectin Vicia villosa agglutinin and Golgi's silver nitrate

This study demonstrates that many neurons in the somatosensory cortex, cingulate cortex, retrosplenial cortex and hippocampal subiculum of the mouse brain are covered by sulfated proteoglycans which are intensely negative-charged and stained with cationic iron colloid, while being digested with hyaluronidase. Neurons with similar perineuronal proteoglycans are also recognized in the extrapyramidal system (superior colliculus, red nucleus, reticular formation, vestibular nuclei and cerebellar nuclei), in the secondary auditory system (cochlear nuclei, nucleus of trapezoid body, inferior colliculus and nucleus of lateral lemniscus), in the vestibulo-ocular reflex system (vestibular nuclei and extraocular motor nuclei), and in the pupillary reflex system. The neurons with perineuronal sulfated proteoglycans in the cerebral cortices and hippocampal subiculum are usually labeled with the lectin Vicia villosa agglutinin, though those in the cerebellar, vestibular and cochlear nuclei may not be reactive to this lectin. Double staining of the retrosplenial cortex, hippocampal subiculum and cerebellar nuclei with Golgi's silver nitrate and cationic iron colloid indicates that the perineuronal sulfated proteoglycans are identical with the Golgi's reticular coating or glial nets.

Perineuronal sulfated proteoglycans in the human brain are identical to Golgi's reticular coating

Many neurons in the human somatosensory cortex (Area 7 of Brodmann) possess an intensely negative-charged surface coat consisting of perineuronal sulfated proteoglycans which were stained with cationic iron colloid. This surface coat was stained doubly with cationic iron colloid and Golgi's silver nitrate. The result indicates that the perineuronal sulfated proteoglycans are identical with Golgi's reticular coating, whose existence and nature have previously been controversial. The result also suggests that Golgi's silver nitrate stains the core proteins of proteoglycans.

NMR studies on water and polymer diffusion in dextran gels. Influence of potassium ions on microstructure formation and gelation mechanism

At room temperature aqueous solutions of dextrans with concentrations > 25% (w/w) exhibit a sol-gel transition in the presence of > 1.0 M potassium chloride. In dextrans the gelation was unexpected due to missing anionic groups that usually provide the binding sites for cations. The quantitative investigation of the gel formation is based on changes of the diffusibility of water and dextran chains. The apparent diffusion coefficients of bulk water (in the order of 10(-6) cm2/s) and of water trapped in the junction zones as well as of polymer chains (in the order of 10(-7) to 10(-8) cm2/s) are determined by employing pulsed field gradient stimulated echo (PFGSTE) NMR. The restricted diffusion of bulk water in viscous sols and in soft and rigid gels has been quantitatively analyzed providing data for interbarrier distances (pore size), permeabilities of the diffusion barriers (density of junction zones) and interbarrier diffusion coefficients of water. Based on already published x-ray structure data and in accordance with the diffusion data presented in this paper "potassium-bonding" is assumed to be the most important interaction for the formation of a microstructure and for the stabilization of cross-links. The ionic radius of the potassium ion perfectly fits to the cage established by six oxygen atoms of glucose units of three polymer chains. Other cations, such as Li+, Na+, Rb+ and Cs+, according to their nonfitting ionic radii, do not provoke dextran gelation under these conditions. The mechanism of the transitions from sol to soft gel and further to rigid gel is discussed on the basis of restricted diffusion and x-ray structure data.