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PubMed1985

Variability in transport rates of secretory glycoproteins through the endoplasmic reticulum and Golgi in human hepatoma cells.

We have previously shown that newly synthesized liver secretory proteins are exported at three distinct characteristic rates, with intracellular retention half-times of 110-120 min (e.g. transferrin), 75-80 min (e.g. ceruloplasmin), and 30-40 min (e.g. alpha 1-protease inhibitor) (J. B. Parent, H. Bauer, and K. Olden (1985) Biochim. Biophys. Acta, in press). In the present study we have determined the average time required for specific glycoproteins to move through the various compartments of the intracellular transport pathway, consisting of endoplasmic reticulum and Golgi complex. Localization in particular compartments was monitored by the use of the following complementary approaches: (i) Percoll density gradient fractionation of the subcellular organelles, (ii) sensitivity of the glycan moiety of N-linked glycosylation to endo-beta-N-acetylglucosaminidase H, and (iii) by the lectin-binding characteristics. The cell fractionation studies revealed that alpha 1-protease inhibitor, ceruloplasmin, and transferrin were transported from the rough endoplasmic reticulum with a retention half-time of 10, 30, or 45 min, respectively. Measurements of the rate at which newly synthesized glycoprotein became endo H-resistant (an event localized near the medial region of Golgi) demonstrated that it took 60-70, 30, and 18 min for 50% of transferrin, ceruloplasmin, and alpha 1-protease inhibitor, respectively, to reach the medial Golgi. Consistent with this finding, maximal binding of transferrin to wheat germ agglutinin (also a medial Golgi event) and Ricinus communis agglutinin I (a trans Golgi event) required 75 and 90 min, respectively, and maximal binding of ceruloplasmin to both lectins occurred in approximately 30 min. Maximal binding of alpha 1-protease inhibitor to wheat germ agglutinin and Ricinus communis agglutinin I required 15 and 30 min, respectively. The results presented here clearly indicate that (i) the time required for protein secretion cannot be entirely accounted for by lag in transport from the rough endoplasmic reticulum to the Golgi since the glycoproteins examined are retained in the former organelle for no more than two-fifths of the total intracellular retention half-time, and (ii) the variability in rates of protein secretion is not due solely to differences in rates of transport from the rough endoplasmic reticulum to the Golgi as variability in retention within the Golgi is also demonstrated. The results are discussed in terms of their compatibility with receptor-mediated transport of glycoproteins in both the endoplasmic reticulum and Golgi.

Biological Transport↗
PubMed1987

Formation of the alpha-bungarotoxin binding site and assembly of the nicotinic acetylcholine receptor subunits occur in the endoplasmic reticulum.

During the process by which newly synthesized subunits of the nicotinic acetylcholine receptor (stoichiometry = alpha 2 beta gamma delta) mature and acquire the properties of the fully functional cell surface receptor, they undergo numerous covalent and noncovalent modifications. Using ligand-mediated and subunit-specific immunoprecipitation, four forms in the maturation of the alpha subunit can be detected: the primary translation product; alpha subunit that can bind alpha-bungarotoxin; alpha subunit assembled with the other subunits; and surface receptor. The alpha subunit acquires the ability to bind alpha-bungarotoxin with a t1/2 of approximately 40 min after translation and becomes assembled with a t1/2 of 80 min after translation. Using metabolic labeling and sucrose gradient fractionation, we have determined the subcellular location of alpha subunit when it acquires the ability to bind alpha-bungarotoxin and when it is assembled. Golgi membranes were identified across the gradient by the enzymatic activities UDP-galactose:N-acetylglucosamine galactosyltransferase and alpha-mannosidase. Endoplasmic reticulum membranes were identified by the enzymatic activity glucose-6-phosphatase and by the presence of newly synthesized alpha and beta subunits. Pulse-labeled alpha subunit that bound alpha-bungarotoxin was first detected co-migrating in the gradient with the glucose-6-phosphatase activity. Therefore, the capacity to bind alpha-bungarotoxin was acquired while the alpha subunit was in the endoplasmic reticulum. Assembled alpha subunit was detected by immunoprecipitating with an anti-beta subunit-specific monoclonal antibody. By this method, assembled receptor was first detected 15 min after translation in both the endoplasmic and Golgi portions of the gradient. To validate this method of detecting assembled receptor, we determined the sedimentation coefficient of the receptor subunits in the endoplasmic reticulum. Both unassembled subunits with sedimentation coefficients of 5 S and assembled receptor with a sedimentation coefficient of 9 S were recovered from the endoplasmic reticulum portion of the gradient. Thus, our data concerning the subcellular site of assembly are consistent with assembly occurring in the endoplasmic reticulum followed by rapid transport to the Golgi.

Binding Sites↗
PubMed1986

Porcine malignant hyperthermia susceptibility: increased calcium-sequestering activity of skeletal muscle sarcoplasmic reticulum.

This study tested the hypothesis that calcium-sequestration by isolated sarcoplasmic reticulum was abnormal in skeletal muscle of malignant hyperthermia-susceptible swine. A heavy sarcoplasmic reticulum fraction was isolated from malignant hyperthermia and control muscle using differential and density-gradient centrifugation. Prior to onset of malignant hyperthermia, calcium-sequestering activity (Vmax at 37 degrees C, mumol calcium/mg/min) was twofold increased in malignant hyperthermia sarcoplasmic reticulum compared to control sarcoplasmic reticulum (1.96 +/- 0.50 versus 4.00 +/- 0.87, P less than 0.01), although thermodynamic and kinetic properties of this activity were otherwise indistinguishable between groups. This increased activity of the malignant hyperthermia sarcoplasmic reticulum fraction was associated with twofold increased concentration of Ca-ATPase and calsequestrin protein. When a malignant hyperthermia-reaction developed, calcium-uptake was depressed to less than 5% of control values. These data indicate that malignant hyperthermia is not initiated due to a defect in the calcium-sequestration mechanism, however, loss of calcium-uptake activity occurring after the onset of malignant hyperthermia might result in the propagation and irreversibility of the malignant hyperthermia reaction.

Animals↗
PubMed1984

Calmidazolium and compound 48/80 inhibit calmodulin-dependent protein phosphorylation and ATP-dependent Ca2+ uptake but not Ca2+-ATPase activity in skeletal muscle sarcoplasmic reticulum.

Two specific calmodulin antagonists, compound 48/80 and calmidazolium , at concentrations of 10-20 micrograms/ml and 10-20 microM, respectively, inhibited Ca2+ uptake in skeletal muscle sarcoplasmic reticulum vesicles without affecting Ca2+-ATPase activity. The drugs also inhibited the calmodulin-dependent phosphorylation of 85,000-, 60,000-, and 20,000-dalton proteins, but not the calmodulin-independent phosphorylation of other sarcoplasmic reticulum proteins. The inhibition of phosphorylation of the 60,000-dalton protein closely paralleled the inhibition of Ca2+ uptake. Neither drug affected the passive permeability of the sarcoplasmic reticulum membrane at concentrations up to 5 times the inhibitory dose, and neither drug inhibited Ca2+ uptake into liposomes reconstituted with the purified Ca2+-ATPase. However, calmodulin-dependent reconstitution of Ca2+ uptake in EGTA-extracted sarcoplasmic reticulum vesicles was inhibited by 48/80. The results of this study suggest that the calmodulin-dependent phosphorylation system plays a functional role in the coupling of ATP hydrolysis and Ca2+ accumulation, perhaps through regulation of Ca2+ release channels in the sarcoplasmic reticulum membrane. Perturbation of phosphorylation by 48/80 and calmidazolium may lead to enhanced Ca2+ release, thereby diminishing Ca2+ accumulation without affecting the Ca2+ uptake mechanism.

Adenosine Triphosphate↗
PubMed1981

Purification and characterization of the 53,000-dalton glycoprotein from the sarcoplasmic reticulum.

A 53,000-dalton intrinsic glycoprotein of the sarcoplasmic reticulum was separated from the Ca2+ + Mg2+-ATPase by dissolution with low concentrations of deoxycholate in the presence of 1 M KCl and purified in two successive gel filtration steps. It was aggregated and eluted at the void volume when subjected to gel filtration in the presence or absence of deoxycholate. When subsequently chromatographed in the presence of sodium dodecyl sulfate, the glycoprotein eluted in pure form as a monomer. The glycoprotein contained 48% nonpolar amino acids. It also contained 4 mol of glucosamine and 18 mol of mannose per mol of protein, suggesting that it contained two chains of (GlcNAc)2, (Man)9. The 53,000-dalton glycoprotein was completely removed from deoxycholate extracts of sarcoplasmic reticulum by affinity chromatography on concanavalin A Sepharose. Elution of glycoproteins with alpha-methyl-D-mannoside and deoxycholate resulted in co-purification of the 53,000-dalton glycoprotein and 160,000-dalton glycoprotein previously observed in sarcoplasmic reticulum. The apparent molecular weight of the glycoprotein was reduced from 53,000 to 49,000 after digestion with endo-beta-N-acetylglucosaminidase H (Endo H) and its reactivity with concanavalin A (Con A) was lost. There was no change in molecular weight of the glycoprotein and no diminution of its reactivity with Con A when sealed vesicles of sarcoplasmic reticulum were treated with Endo H. Endo H reduced the molecular weight and the Con A reactivity of the protein when the vesicles were made permeable by detergents. These observations, together with our previous demonstration that the glycoprotein reacts with a cycloheptaamylose-fluorescamine complex in sealed vesicles (Michalak, M., Campbell, K. P., and MacLennan, D. H. (1980) J. Biol. Chem. 255, 1317-1326), show that the glycoprotein is a transmembrane protein. A protein of approximately 53,000 daltons was labeled when the sarcoplasmic reticulum was reacted with the photoaffinity label [32P]8-N3-cAMP. The labeled protein was neither the glycoprotein nor the high affinity calcium-binding protein since it was not sensitive to Endo H and was sensitive to trypsin digestion.

Affinity Labels↗
PubMed1980

The biosynthesis of sarcoplasmic reticulum.

Muscle differentiation provides a slow-motion picture of the assembly of highly specialized sarcoplasmic reticulum endowed with Ca2+ transport activity from its constituents. During development of chicken embryo pectoralis muscle, the sarcoplasmic reticulum evolves from the rough endoplasmic reticulum of myoblasts by insertion of Ca2+ transport ATPase molecules synthesized on membrane-bound polysomes into the phospholipid-rich endoplasmic reticulum membrane. The process continues until the Ca2+ ATPase content of the membrane approaches physical saturation. The rate of synthesis of Ca2+ ATPase sharply increases after fusion of myoblasts into multinucleated myotubes and the accumulation of sarcoplasmic reticulum and myofibrillar proteins follows a roughly similar time course. The regulation of Ca2+ ATPase synthesis during development involves myogenic as well as neurogenic mechanisms. There are indications that changes in intracellular free Ca2+ concentration may play a role in this regulation.

Animals↗
PubMed1980

Transient kinetics of a Ca2+-induced fluorescence change from membrane-associated and solubilized sarcoplasmic reticulum Ca2+-ATPase.

The kinetics and extent of the fluorescence change induced by Ca2+ interaction with the Ca2+-ATPase from sarcoplasmic reticulum have been compared by stopped flow fluorimetry for three preparations: sarcoplasmic reticulum; purified ATPase in membrane vesicles; and solubilized, delipidated ATPase. The kinetics of Ca2+ release and binding for both purified preparations could be described by a single exponential as has been observed for sarcoplasmic reticulum. The rate and extent of the fluorescence change for the solubilized and membrane-associated preparations are shown to be quite similar to those of the sarcoplasmic reticulum. From these results, it is concluded that all of the Ca2+-induced fluoescence change in sarcoplasmic reticulum originates from the Ca2+-ATPase. In addition, since the change in fluorescence is probably result of a conformational change in the ATPase during the Ca2+ pumping cycle, the results provide additional evidence that monomeric Ca2+-ATPase may be capable of Ca2+ transport since the delipidated preparation is monomeric under the conditions used for these experiments. Finally, it is concluded that phospholipid bilayer is not essential for this conformational change.

Animals↗
PubMedDate not supplied

The phenomenon of reversal of reticulum action potentials recorded from the body surface of sheep.

The experiments were carried out on sheep with reticulum fistula. The biopotentials and transformed mechanogram of the reticulum were recorded simultaneously on the body surface with an electrocardiograph. Lactic acid solution 1.6 mol/l was administered through the fistula into the reticulum in an amount of 15 mmol/kg of body weight. It was found that administration of this acid caused reversal of the biopotentials of the reticulum. This phenomenon lasted from 10 to several scores of hours and occurred with pH of reticulum contents below the normal range as well as after return of normal pH.

Action Potentials↗
PubMed1983

Unusual configurations of endoplasmic reticulum in human pituitary adenomas.

Electron microscopic study of 435 surgically-removed human pituitary adenomas and 43 nontumorous adenohypophyses revealed unusual configurations of endoplasmic reticulum in 102 adenohypophysial tumors (23%) and in 12 nontumorous adenohypophyses (28%). These configurations classified as paired reticulum, annulate lamellae and ribosome-lamellar complexes were noted in various adenomatous and nontumorous adenohypophysial cells, indicating that they could not be used as specific markers for pituitary adenomas or for a particular adenohypophysial cell type. Paired reticulum was a common finding, whereas annulate lamellae and ribosome-lamellar complexes were rarely encountered. Whether or not these endoplasmic reticulum configurations could be considered as normal constituents of adenohypophysial cells was difficult to assess, since nontumorous cells studied were from patients who had various diseases and who had been treated with different hormones. The presence of endoplasmic reticulum configurations was neither related to age, sex of the patients nor degree of differentiation or endocrine activity of pituitary adenomas.

Adenoma↗
PubMed1982

Physical separation and biochemical characterization of H-2b-encoded proteins on target cell plasma membranes and endoplasmic reticulum.

Plasma membranes and endoplasmic reticulum were purified on the basis of their physical properties, and their identity was confirmed by membrane marker activities. Comparative adsorption analysis indicated that plasma membrane and endoplasmic reticulum vesicle fractions adsorbed 25% and 5%, respectively, as much anti-D6 alloantiserum as intact cells. Two-dimensional gel analyses of immunoprecipitates of the H-2b-encoded proteins from the EL4 tumor cell line indicated a series of proteins containing complex carbohydrates in the plasma membrane and two additional N-asparagine-linked proteins in the endoplasmic reticulum. Both neuraminidase and protein phosphatase treatments were required to convert the mobilities of the plasma membrane forms of the H-2Kb and H-2Db antigens in two-dimensional gel electrophoresis to the mobilities of the endoplasmic reticulum forms. The endoplasmic reticulum form of H-2Db was shown to contain three N-asparagine-linked carbohydrates by endoglycosidase H treatment.

Animals↗
PubMed1981

Mode of action of prilocaine on sarcoplasmic reticulum in skinned skeletal muscle fibers.

Single fibers were isolated from the semitendinosus muscle of a frog and the skinned fibers were prepared by the removal of the sarcolemma. In the range of several millimolar concentrations, prilocaine caused a contracture of the single fibers in both polarized and depolarized states. It also induced Ca++ release from the sarcoplasmic reticulum and depressed Ca++ uptake by the sarcoplasmic reticulum. Prilocaine increased the release of Ca++ with increasing concentration, but, unlike caffeine, prilocaine could not enhance the Ca++-induced Ca++ release mechanism of the sarcoplasmic reticulum. Like a depolarization-induced Ca++ release, the prilocaine-induced Ca++ release was not inhibited by Mg++, whereas it was inhibited by sucrose. The Ca++ release induced with prilocaine occurred only immediately after the application; thereafter the Ca++ release mechanism seemed to be inactivated by the prolonged presence of the drug. A similar inactivation in the mechanism of prilocaine-induced Ca++ release also occurred when the extent of depolarization of the sarcoplasmic reticulum membrane increased. These results suggest that the mode of action of prilocaine on the sarcoplasmic reticulum could be a depolarization-like action.

Animals↗
PubMed1994

Prostacyclin analog (cicaprost) protects against damage by hydrogen peroxide to rabbit cardiac sarcoplasmic reticulum.

The membrane fluidity of the cardiac sarcoplasmic reticulum in rabbit was monitored by measuring changes in steady-state fluorescence anisotropy (rs) using diphenylhexatriene as a probe. The Ca(2+)-ATPase activity of the sarcoplasmic reticulum was measured by assaying the amount of inorganic phosphate released from ATP. Hydrogen peroxide caused damage to the sarcoplasmic reticulum, as reflected by decreases in membrane fluidity and Ca(2+)-ATPase activity. The damage caused by hydrogen peroxide was completely prevented by 20 micrograms/ml catalase. Cicaprost (240 nM) provided an effective protection against injury to the sarcoplasmic reticulum caused by exposure to hydrogen peroxide. The rs value was significantly decreased from 0.154 +/- 0.014 to 0.122 +/- 0.005 (p < 0.01). Ca(2+)-ATPase activity was increased from 3.1 +/- 1.31 to 18.87 +/- 2.11 microM phosphate/mg protein/hour (p < 0.01). The protection given by cicaprost was dose dependent. We conclude that cicaprost protects against damage produced by hydrogen peroxide in cardiac sarcoplasmic reticulum in the rabbit. The mechanism of the effect of cicaprost remains to be elucidated.

Animals↗
PubMed1993

[Calcium release channel of cardiac muscle sarcoplasmic reticulum].

Cardiac muscle contractility is controlled by myoplasmic calcium (Ca) concentration. Sarcoplasmic reticulum plays an essential role in the regulation of [Ca]. Depolarization of the sarcolemma induces Ca release from the sarcoplasmic reticulum, leading to the muscle contraction. On the other hand, Ca uptake by the sarcoplasmic reticulum into the lumen results in the muscle relaxation. The Ca release from the sarcoplasmic reticulum is mediated by Ca release channel. Using ryanodine as a molecular probe, the calcium release channel has been isolated, purified and characterized. Morphological studies have confirmed its identity with the feet structure which spans between the transverse tubule and the junctional face of the sarcoplasmic reticulum. The cardiac Ca release channel cDNA encodes 4969 amino acids with a molecular weight of 564,711. The analysis of the sequence indicates that 10 potential transmembrane sequences in the COOH-terminal fifth of the molecule and two additional nearer to the center of the molecule could contribute to the formation of the Ca conducting pore. The remainder of the molecule is hydrophilic and constitutes the cytoplasmic domain which corresponds to the feet structure. Northern blot analysis has shown that the cardiac Ca release channel is expressed in heart and brain. The channel is modulated by Ca, ATP, calmodulin, and phosphorylation. A potential modulator binding domain has been identified in the molecule by searching consensus sequences and investigation of a causal mutation for malignant hyperthermia, the primary defect of which exists in the skeletal Ca release channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Histochemistry of sarcoplasmic reticulum Ca-ATPase using dysprosium as capturing reagent.

This report describes the development of a histochemical method for the demonstration of sarcoplasmic reticulum Ca-ATPase activity in cross-sections of skeletal muscle. The demonstration of sarcoplasmic reticulum Ca-ATPase activity is complicated by the fact that capturing reagents for phosphate inhibit the enzyme. We present a minimal model for heavy-metal-phosphate precipitation reactions which gives a theoretical description of the effect of enzyme inhibition on the rate of phosphate precipitation in the section. The model indicates that the choice of capturing reagent is crucial: whether or not ATPase activity can be demonstrated depends mainly on the inhibition constant and the solubility product of the phosphate salt of the capturing reagent (but also on a fairly large number of other factors). All lanthanides tested can be used to demonstrate sarcoplasmic reticulum Ca-ATPase activity, but dysprosium results in the highest staining intensity. This suggests that dysprosium inhibits sarcoplasmic reticulum Ca-ATPase to a lesser degree than the other lanthanides and/or the solubility product of its phosphate salt is smaller. As an example, the method is used to investigate the effect of thyroid hormone on sarcoplasmic reticulum Ca-ATPase activity in individual fibres of the rat soleus muscle.

Animals↗
PubMed1996

The decompensated detrusor II: evidence for loss of sarcoplasmic reticulum function after bladder outlet obstruction in the rabbit.

PURPOSE: While it may lack the classic morphological pattern in striated muscle systems, there is ample evidence that smooth muscle also contains sarcoplasmic reticulum. These intracellular storage sites release calcium into the cytosol to generate contractile force in response to various stimuli. A major component of the sarcoplasmic reticulum is an adenosine triphosphate dependent ion pump, which serves to drive free calcium out of the cytosol back into this intracellular reservoir. This ion pump serves to maintain the intracellular calcium storage sites, and also as a marker of the sarcoplasmic reticulum. MATERIALS AND METHODS: Muscle strip studies were performed to stratify the data into 3 major groups (controls, and compensated and decompensated obstructions) based on physiological performance. These were correlated with biochemical and molecular determinations of sarcoplasmic endoplasmic reticulum calcium, magnesium-adenosinetriphosphatase expression. RESULTS: Our results demonstrate a remarkable loss of sarcoplasmic endoplasmic reticulum calcium-adenosinetriphosphatase activity in the decompensated group and a moderate loss in the compensated group. CONCLUSIONS: These data provide molecular support for our previous physiological studies in which we demonstrated an important role for intracellular calcium storage and release with normal bladder smooth muscle function. These data strongly support our contention that contractile dysfunction in bladder smooth muscle following outlet obstruction is partially mediated by changes in the mechanisms of intracellular calcium homeostasis.

Animals↗
PubMed1996

Acylphosphatase stimulates Ca2+ transport and Ca(2+)-dependent ATPase activity in cardiac sarcoplasmic reticulum.

Acylphosphatase purified from heart muscle actively hydrolyzes the phosphoenzyme intermediate of cardiac sarcoplasmic reticulum Ca(2+)-ATPase. This effect was evident with acylphosphatase concentrations (up to 100 units/mg sarcoplasmic reticulum protein) that fall within the physiological range, and the low value of the apparent Km, on the order of 10(-7)M, suggests a high affinity towards this special substrate. Moreover, acylphosphatase addition to sarcoplasmic reticulum vesicles significantly enhanced the rate of Ca(2+)-dependent ATP hydrolysis. Maximal stimulation, observed with 100 units/mg vesicular protein, resulted in an ATPase activity which was about two folds over basal value. The same acylphosphatase concentration increased at a similar extent the rate of ATP driven Ca2+ influx into sarcoplasmic reticulum vesicles. Taken together these findings lead to suppose that acylphosphatase, owing to its hydrolytic activity, induces an accelerated turnover of the phosphoenzyme intermediate, whence an overall stimulation of heart sarcoplasmic reticulum Ca2+ pump, affecting both ATP hydrolysis and Ca2+ influx.

Acid Anhydride Hydrolases↗
PubMed1980

Neuronal transport of acid hydrolases and peroxidase within the lysosomal system or organelles: involvement of agranular reticulum-like cisterns.

Neurosecretory neurons of the hyperosmotically stressed hypothalamo-neurohypophysial system have been a useful model with which to demonstrate interrelationships among perikaryal lysosomes, agranular reticulum-like cisterns, endocytotic vacuoles, and the axoplasmic transport of acid hydrolases and horseradish peroxidase. Supraoptic neurons from normal mice and mice given 2% salt water to drink for 5--8 days have been studied using enzyme cytochemical techniques for peroxidase and lysosomal acid hydrolases. Peroxidase-labeling of these neurons was accomplished by intravenous injection or cerebral ventriculocisternal perfusion of the protein as previously reported (Broadwell and Brightman, '79). Compared to normal controls, supraoptic cell bodies from hyperosmotically stimulated mice contained elevated concentrations of peroxidase-labeled dense bodies demonstrated to be secondary lysosomes and acid hydrolase-positive and peroxidase-positive cisterns either attached or unattached to secondary lysosomes. These cisterns were smooth-surfaced and 400--1,000 A wide. Their morphology was similar to that of the agranular reticulum. Some of the cisterns contained both peroxidase and acid hydrolase activities. The cisterns probably represent an elongated form of lysosome and, therefore, are not elements of the agranular reticulum per se. By virtue of their direct connections with perikaryal secondary lysosomes, these cisterns may provide the route by which acid hydrolases and exogenous macromolecules can leave perikaryal secondary lysosomes for anterograde flow down the axon. Very few smooth-surfaced cisterns were involved in the retrograde transport of peroxidase within pituitary stalk axons from normal and salt-treated mice injected intravenously with peroxidase. Peroxidase undergoing retrograde transport was predominantly in endocytotic structures such as vacuoles and cup-shaped organelles, which deliver this exogenous macromolecule directly to secondary lysosomes for degradation in the cell body. These observations extend our previously reported findings in the axon to the cell body and suggest that agranular reticulum-like cisterns in the perikaryon, like those in the axon, may be part of the lysosomal system rather than associated with the agranular reticulum. A diagram summarizing the lysosomal system of organelles and proposed transport of acid hydrolases and peroxidase in neurosecretory neurons specifically and in neurons in general is provided.

Animals↗
PubMed1988

Interdigitating reticulum cells in the dermal infiltrate of mycosis fungoides. An ultrastructural and immunohistochemical study.

In order to provide insight into the role of accessory cells in lymphoproliferative neoplasms, 7 cases of mycosis fungoides at various clinical stages--patches, plaques and nodules--were studied ultrastructurally and immunohistochemically. The aim was to establish whether interdigitating reticulum cells are a constant finding in the dermal infiltrate. Their possible relationships with mycosic cells were also investigated. This study revealed that interdigitating reticulum cells were present in all the skin lesions examined, were present in considerable number in the patches and plaques and became sparse in the nodules. Furthermore, in the lesions at various clinical stages these cells showed varying ultrastructural features, probably related to different developmental stages. The close contacts between interdigitating reticulum cells and mycosic cells, the expression of antigenic markers of activation by mycosic cells and the morphological and immunohistochemical signs of progressive de-differentiation of mycosic cells in the more advanced stages suggest that interdigitating reticulum cells are involved in stimulating proliferation and--possibly--neoplastic progression of mycosic cells. A role for the T-cell microenvironment created in the dermis by lymphoid infiltrate in inducing the differentiation of interdigitating reticulum cells from their precursors is proposed.

Adult↗