Biomedical subjects

L E Ericson

Publications and source records attributed to L E Ericson.

At least 19 recordsLinked to original sources

PubMed1996

Ca2+-dependent and Ca2+-independent regulation of the thyroid epithelial junction complex by protein kinases.

The integrity of epithelial cell junctions is controlled by E-cadherin-mediated (Ca2+-dependent) cell-cell adhesion. In thyroid follicular cells the dissociation of junctions induced by transfer to low Ca2+ medium (Ca2+ switch) is prevented by thyrotropin acting via cyclic AMP/protein kinase A (cAMP/PKA) (Nilsson et al., Eur. J. Cell Biol. 56, 308-318, 1991). In MDCK kidney epithelial cells protein kinase inhibitors elicit a similar response which, however, is cadherin-independent (Citi, J. Cell Biol. 117,169-178,1992; Citi et al., J. Cell Sci. 107, 683-692, 1994). As such inhibitors also may interfere with PKA, we examined in a single cell type, filter-cultured pig thyrocytes, the effects and possible interactions of the cAMP/PKA agonist forskolin (or thyrotropin) and the kinase inhibitor H-7 in Ca2+ switch experiments. We found that the epithelial barrier dysfunction, comprising loss of transepithelial resistance, increased transepithelial flux of [3H]inulin and redistribution of junction proteins (cadherin and ZO-1), which follows Ca2+ removal were inhibited by TSH, forskolin, and H-7. All agents were also able to induce recovery of resistance in low Ca2+. The maximal recovery effects of forskolin and H-7 were additive when given simultaneous with Ca2+ chelator. In contrast, forskolin-induced recovery initiated 10 min after Ca2+ removal was antagonized by H-7. The protection of junctions by forskolin in low Ca2+ was rapidly abolished by light trypsinization (0.001%), whereas the same concentration of trypsin had little or no effect on the corresponding action of H-7 or staurosporine, another potent kinase inhibitor. In H-7-treated cells kept in low Ca2+, trypsin caused redistribution of ZO-1 from the plasma membrane to the cytoplasm while the transepithelial resistance remained high. Taken together, the data indicate that TSH via cAMP/PKA and the protein kinase inhibitor H-7 reinforce the thyroid epithelial barrier under low Ca2+ conditions by distinct although interacting mechanisms. The high sensitivity to proteolysis in the absence of Ca2+ suggests that the cAMP-regulated mechanism is cadherin-dependent. H-7 promotes or inhibits the cAMP/PKA-mediated recovery of transepithelial resistance depending on the duration of the preceding low Ca2+ period. The trypsin-induced displacement of ZO-1 in H-7-treated cells in low Ca2+ suggests that the localization of ZO-1 to the tight junction is not necessary for the maintenance of junctional tightness.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1996

Immunohistochemical studies on the distribution of albumin, fibrinogen, fibronectin, IgG and collagen around PTFE and titanium implants.

Time-dependent distribution of extracellular proteins (albumin, fibrinogen, fibronectin, collagen-I and IgG) in the interface zone between implant and soft tissue has been investigated utilizing a recently developed method. Commercially pure (c.p.) titanium and polytetrafluoroethylene (PTFE) implants were inserted in the abdominal wall of rats for 1, 6 and 12 weeks followed by a mild fixation, cryoprotection, rapid freezing in LN2-cooled propane, cryosubstitution and low-temperature infiltration with UV curing of the methacrylate LR-Gold. Before sectioning, the bulk part of the titanium was removed by an electrolytical dissolution technique (electropolishing), while the PTFE implants were removed by a fracture technique. Employing a cryosubstitution method combined with postembedding immunohistochemistry, a light microscopic analysis was allowed. The selected proteins had an apparently varying distribution in the implant-close tissue and their distribution changed during the follow-up period. There was also a difference in the distribution pattern for each protein around titanium and PTFE implants. Insertion of the c.p. titanium implants elicited an inflammatory reaction in many respects similar to a normal wound healing response, while the PTFE implants caused a more pronounced, persistent inflammation.

Abdominal Muscles↗

PubMed1996

Monocyte activation on titanium-sputtered polystyrene surfaces in vitro: the effect of culture conditions on interleukin-1 release.

The release of interleukin-1 alpha (IL-1 alpha) by human peripheral blood monocytes cultured for 24 and 48 h on polystyrene (PS) and titanium-sputtered polystyrene (Ti) was evaluated. Magnetron sputtering of the PS surfaces resulted in a formation of a 50-nm-thick coat, consisting of an outer layer of TiO2. Monocytes released IL-1 alpha without the addition of exogenous stimuli. A doubling of the culture time from 24 to 48 h did not have a major effect on the amount of IL-1 alpha released. The IL-1 alpha levels were increased by addition of lipopolysaccharide (LPS). High concentrations of PS particles (1 and 3 microns diameter) were equally effective stimuli for IL-1 alpha release as LPS. Preadsorption of fibronectin to culture plates augmented LPS-stimulated IL-1 alpha secretion, whereas preadsorbed fibrinogen had an inhibitory effect. Our observation indicate a direct activation of monocytes by PS and Ti, resulting in IL-1 alpha secretion, which is modified by protein adsorption and exogenous stimuli.

Adsorption↗

PubMed1996

Bone response to surface-modified titanium implants: studies on the early tissue response to machined and electropolished implants with different oxide thicknesses.

The bone formation around titanium implants with varied surface properties is investigated. Machined and electropolished samples with and without thick, anodically formed surface oxides were prepared, surface characterized and inserted in the cortical bone of rabbits (1, 3 and 6 weeks). Scanning electron microscopy, scanning Auger electron spectroscopy and atomic force microscopy revealed marked differences in oxide thickness, surface topography and roughness, but no significant differences in surface chemical composition, between the different groups of implants. Light microscopic morphology and morphometry showed that all implants were in contact with bone and had a large proportion of bone within the threads at 6 weeks. The smooth, electropolished implants, irrespective of anodic oxidation, were surrounded by less bone than the machined implants after 1 week. After 6 weeks the bone volume as well as the bone-implant contact were lower for the merely electropolished implants than for the other three groups. Our study shows that a high degree of bone contact and bone formation are achieved with titanium implants which are modified with respect to oxide thickness and surface topography. However, the result with the smooth (electropolished) implants indicates that a reduction of surface roughness, in the initial phase, decreases the rate of bone formation in rabbit cortical bone.

Animals↗

PubMed1996

Effects of insulin-like growth factor I on growth, epithelial barrier and iodide transport in polarized pig thyrocyte monolayers.

The effects of insulin-like growth factor I (IGF-I) on mitogenesis, epithelial barrier function and transepithelial iodide transport were studied in confluent, polarized monolayers of pig thyrocytes cultured on filter in Transwell bicameral chambers. The growth rate in controls cultured in 1% fetal calf serum was low. Insulin-like growth factor I stimulated dose-dependently the incorporation of [3H]thymidine, maximally at 100 ng/ml, which corresponded to an increase of DNA content by 60% after 6 days. Thyrotropin (1 mU/ml) alone did not stimulate cell multiplication but inhibited partially the stimulatory effect of IGF-I. Insulin-like growth factor I (100 ng/ml) increased within 10 min the transepithelial potential difference, which remained elevated for several days, but did not significantly change the transepithelial resistance. When added together, IGF-I reinforced the effects of TSH on potential difference (increase) and resistance (decrease). A preserved epithelial barrier in IGF-I-treated cultures was confirmed by observing a normal immunolocalization of the tight junction protein ZO-1 and an unchanged ultrastructure of the junctional complex. Insulin-like growth factor I increased the transepithelial flux of 125I- in the basal-to-apical, but not in the opposite, direction. Stimulation of iodide transport by IGF-I was modest after 2 days and pronounced after 6 days. In comparison, TSH-stimulated iodide transport was higher after 2 days but lower after 6 days. Both TSH and IGF-I were strongly synergistic, after 6 days amounting to a 90-fold increase over the control basoapical 125I- transfer. The simultaneous accumulation of 125I- in the cell layer was increased two- to fourfold by IGF-I and/or TSH. In conclusion, IGF-I is able to induce growth in preformed monolayers of pig thyrocytes cultured on permeable filter. During these conditions, the mitogenic effect of IGF-I is partially inhibited by TSH, which has no growth-promoting action on its own. The transepithelial transport of iodide and bulk electrolytes is altered by IGF-I without affecting the epithelial barrier function. Specifically, IGF-I up-regulates the activity of the basolateral iodide pump and increases the iodide permeability of the apical plasma membrane. The action of IGF-I on iodide transport is independent of, although synergistic with, that of TSH. The findings support the notion that IGF-I may be an important regulator of thyroid growth and differentiated functions.

Animals↗

PubMed1996

Primary culture of human thyrocytes in Transwell bicameral chamber: thyrotropin promotes polarization and epithelial barrier function.

Epithelial properties of thyrocytes are difficult to maintain in conventional cell culture systems. We used bicameral chambers (Transwell) in attempts to establish a functional epithelium of thyrocytes of human origin. Thyroid follicle segments were isolated by collagenase digestion of paradenomatous tissue obtained at surgery for follicular adenoma and of tissue from glands with Graves' disease. After careful separation from connective tissue and single cells by centrifugation, the follicles were plated at high density on the collagen-coated filter of the chambers and cultured in Eagle's essential medium (EMEM) containing 10% fetal calf serum (FCS) or Coon's modified Hams medium enriched with five or six factors (5H, 6H); the latter media contained 5% FCS without (5H) or with (6H) thyrotropin (TSH). The follicles were converted into a confluent cell layer, which had similar DNA content irrespective of type of medium, after 4-6 days. Cells grown in EMEM or 5H established a transepithelial electrical resistance (R) of 200-500 omega.cm2 and was impermeable to [3H]inulin, indicating the formation of epithelial junctions. Addition of 6H to confluent cells initially cultured in EMEM or 5H caused a further increase of R, maximally to 1500 omega.cm2, along with a rise of the transepithelial potential difference; 6H promoted the monolayer formation of cells, increased the number of apical microvilli and reinforced the junctional distribution of actin, cadherin and ZO-1; 6H also enhanced the polarized secretion of [3H]leucine-labeled thyroglobulin into the apical medium. Cells from Graves' thyroid tissue established an epithelium on the filter with similar characteristics to that of normal thyrocytes; some platings contained in addition large numbers of HLA-DR positive cells with a dendritic shape. HLA-DR expression was generally absent in EMEM-or 5H-grown thyrocytes, but appeared in limited areas of the cell layer after 6H and was expressed by all epithelial cells after interferon-gamma stimulation for 48 h. We conclude that human thyrocytes form a tight and polarized epithelium when cultured on permeable filters. The polarized structure and function of the cells are positively regulated by TSH. The culture system may be useful in studies addressing the role of the epithelial phenotype (cell polarity and tight barrier) in normal thyroid function as well as in pathological processes in the thyroid, such as autoimmunity, cell transformation and tumor progression.

Cell Polarity↗

PubMed1995

Effects of epidermal growth factor and phorbol ester on thyroid epithelial integrity.

The effects of epidermal growth factor (EGF) and phorbol ester (tetra-O-decanoylphorbol-16-acetate; TPA) on thyroid epithelial integrity were studied in filter-cultured monolayers of porcine thyrocytes, which before experiments were growth-arrested and had a high transepithelial resistance (RTE > 6.10(3) omega.cm2) and polarized, thyroid-specific functions. Both EGF and TPA stimulated dose-dependently the cellular incorporation of [3H]thymidine, which maximally (at 10 ng/ml EGF for 48 h) corresponded to a 65% increase of the DNA content. The EGF-treated cells proliferated mainly within the original monolayer, which became folded due to the increased cell number; clusters of epithelial cells also assembled between the monolayer and the filter. Although the transepithelial potential difference was reduced, from 15-30 mV in controls to 2-10 mV, the epithelial barrier function was maintained (RTE 1-3.10(3) omega.cm2; impermeability to [3H]inulin). EGF did not change the ultrastructural polarity of the plasma membrane or the distinct distribution of ZO-1 and cadherin immunoreactivities to junctions, but cytoplasmic cadherin present in controls disappeared after EGF. In cultures acutely depleted of extracellular Ca2+ EGF pretreatment for 48 h antagonized the preventive effect of thyrotropin on paracellular leakage and loss of cell-cell adhesion. TPA (0.1 microM) induced a temporary barrier dysfunction (maximal after 24 h) accompanied by pronounced alterations of cell shape and actin-based cytoskeleton, dissociation of junctional cadherin, and shedding of cells into the apical medium. In long-term (2-5 days) TPA-treated cultures the epithelial morphotype and barrier function recovered. The combined stimulation with EGF and TPA caused a persistent derangement of the cell layer including attenuation of ZO-1 at cell-cell contacts, paracellular leakage of [3H]inulin, and cell detachment. We conclude that EGF is able to release porcine thyroid epithelial cells from contact inhibition of growth along with intact cell polarity and tight junctions. Yet, when acting together with phorbol ester EGF provokes a lasting morphological transformation. Impaired positive control of Ca(2+)-dependent cell-cell adhesion in EGF-treated cultures suggests a latent defect with possible transforming potential in the cadherin-based regulation of the junctional complex.

Animals↗

PubMed1995

Electron microscopic observations on the soft tissue around clinical long-term percutaneous titanium implants.

Percutaneous implants of titanium ad modum Brånemark have been in clinical use in the head and neck since 1977. The incidence of adverse reactions is low. In a previous study we have demonstrated the presence of inflammatory cells in the subcutaneous connective tissue surrounding the implants and this increased exposure to exogenous antigens was suggested to be compensated by a barrier of inflammatory cells in the soft tissue. To get further information on the nature of the tissue-implant contact, in the present study we have examined the structure of the tissue close to the percutaneous implant using transmission electron microscopy. We could not see evidence for an attachment of the epithelium to the implant, nor between the connective tissue and the implant. Retrieved implants were also analysed and we did not find any organized tissue remaining on the implants.

Adult↗

PubMed1994

Bone response to surface modified titanium implants: studies on electropolished implants with different oxide thicknesses and morphology.

In a series of experimental studies, bone formation was analysed around systematically modified titanium implants. In the present study, machined, electropolished and anodically oxidized implants were prepared, surface characterized and inserted in the cortical bone of rabbits (7 wks and 12 wks). SEM, scanning Auger electron spectroscopy and atomic force microscopy revealed no differences in surface composition but marked differences in oxide thickness, surface topography and roughness. Light microscopic morphology and morphometry showed that all implants were in contact with bone, and had a large proportion of bone within the threads. The smooth, electropolished implants were surrounded by less bone than the machined implants with similar oxide thickness, (4-5 nm) and the anodically oxidized implants with thicker oxides (21 nm and 180 nm, respectively) after 7 wks. These studies show that a high degree of bone contact and bone formation can be achieved with titanium implants which are modified with respect to oxide thickness and surface topography. However, it appears that a reduction of surface roughness may influence the rate of bone formation in rabbit cortical bone.

Animals↗

PubMed1994

Method for immunolocalization of extracellular proteins in association with the implant-soft tissue interface.

A method allowing immunolocalization of macromolecules surrounding biomaterial implants has been developed. Plugs of pure titanium were inserted into the abdominal wall of rats. One week after implantation plugs with adjacent tissue were gently fixed and cryoprotected before being rapidly frozen in LN2-cooled propane, followed by cryosubstitution, using methanol, and low temperature infiltration and UV curing of the methacrylate LR-Gold. Before sectioning, bulk metal was removed electrochemically, leaving the surface oxide intact, appearing in sections as a dense line in contact with the tissue. Postembedding immunolocalization for rat albumin, IgG, C3c, fibrinogen and fibronectin was performed at the light and electron microscopic levels. Our observations indicate that 1 wk after implant insertion, a network of fibrin and fibronectin decorates the tissue surface that faces the implant, but without any obvious concentration to the implant surface.

Abdominal Muscles↗

PubMed1994

Effects of epidermal growth factor on basolateral iodide uptake and apical iodide permeability in filter-cultured thyroid epithelium.

The effect of epidermal growth factor (EGF) on vectorial iodide (I-) transport was studied in an in vitro model of the polarized porcine thyroid follicular epithelium in Transwell culture chambers. In this model, two mechanisms responsible for the unidirectional transport of I- from the basal to the apical chamber compartments, corresponding to the interstitium to lumen direction in vivo, are present in opposite plasma membrane domains of the tight cell monolayer: a basolateral I- pump and an apical I- efflux mechanism, both regulated by TSH. The cultures were treated with EGF (10 ng/ml) with or without TSH (0.1 mU/ml) for 48 h, and then analyzed for 1) cellular uptake of 125I-, 2) transepithelial 125I- flux (FTE 125I-; basoapical and apicobasal directions) during continuous exposure to 125I- in either the basal or apical medium, and 3) bidirectional (apical and basal) efflux in 125I(-)-loaded cells. Iodination was prevented by methimazole (0.5 mM). EGF increased cell number 25-50%, but did not disturb the tightness or structural polarity of the original cell monolayer. EGF reduced the basal rate and inhibited the TSH-induced long term up-regulation of FTE 125I- across the cell layer in the basoapical direction. However, the radioactivity content of EGF-treated cultures exposed to 125I- in the basal medium was 3-5 times higher than that in controls; apical uptake of 125I- was negligible. The radioiodide accumulated in EGF-treated cells was predominantly released (approximately 80%) in the basal direction, whereas in controls, the ratio of apical to basal 125I- efflux was 3:2. Acute stimulation of EGF-treated cultures with TSH (10 mU/ml) or forskolin (50 microM) caused, as in controls, an increase in apical, but not basal, 125I- efflux within minutes; the peak value of stimulated apical efflux was 10-fold over the prestimulatory level of basoapical FTE 125I- in the same culture. Moreover, the steady state level of basoapical FTE 125I- after the transient efflux peak was higher than that before stimulation and, in fact, approached the corresponding flux in untreated cells. In contrast, in control and TSH-pretreated cultures, the 125I- efflux peak was less pronounced, and the pre- and poststimulatory levels of basoapical FTE 125I- were about equal. FTE 125I- in the apicobasal direction was always low and unresponsive to acute stimulation regardless of pretreatment. In conclusion, EGF-treated porcine thyroid epithelial cells in Transwell culture, despite being released from contact inhibition of growth, are able to concentrate I- and release their I- content in response to acute TSH stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Adherence of RFD-1 positive dendritic cells to the basal surface of thyroid follicular cells in Graves' disease.

HLA-DR positive cells infiltrating Graves' thyroid tissue were examined for their expression of cell-specific immunological markers using light and electron microscopic immunostaining of frozen sections and isolated open thyroid follicles. Graves' glands (n = 21) were enriched of CD68 and Leu-M5/CD11c positive monocytes/macrophages as well as CD4 and CD8 lymphocytes. These cell types were distributed juxta-follicular as well as in other tissue areas. Only the RFD-1 antibody, considered to label antigen-presenting cells including dendritic cells, identified cells invariably located close to the interstitial follicular surface. After follicle isolation, RFD-1 cells were enriched compared to Leu-M5 cells and exclusively adherent to the follicular epithelium. The plasma membrane of RFD-1 positive cells were in intimate contact with the basolateral membrane of the thyrocytes, sometimes extending deeply into the intercellular space of the epithelium. Parallel labelling experiments suggested that the follicle-adhering RFD-1 cells also expressed HLA-DR. Our findings show that in human thyroid glands with Graves' disease RFD-1 positive cells with a dendritic morphology establish direct contact with the follicular epithelium. In view of the fact that both HLA-DR and RFD-1 are associated with antigen-presenting functions it is suggested that a direct interaction of dendritic cells with thyrocytes might be an important component of the autoimmune reaction in Graves' disease.

Antibodies, Monoclonal↗

PubMed1994

A morphometric method to evaluate angiogenesis kinetics in the rat mesentery.

The mesenteric window angiogenesis assay permits the objective determination of a number of angiogenesis parameters in peritoneal connective tissue. The time-course of the angiogenic response that follows activation of endogenous connective tissue mast cells in situ in normal adult rats was investigated using a set of quantitative variables. A method developed to quantify angiogenesis kinetics by evaluation of microvascular ramification and elongation is presented. The angiogenic process was found to proceed long after the termination of the inducing selective mast-cell activation and was thus to a large extent self-perpetuating. The angiogenesis also continued long after the maximum level of the ingrowth of vessels from adjacent tissues, the vessel density, and ramification within the vascularized areas was reached. The whole angiogenic phase lasted as long as 5-6 weeks and the total vessel density, i.e. the vascular area multiplied by the vessel density, remained elevated over controls throughout the course of the 99-day experiment. It appears that angiogenesis kinetics based on truly quantitative assessment of relevant parameters, as in the present study, will be a useful means in elucidating how positive and negative angiogenic factors, individually or in combination, influence the microvascular arborization.

Animals↗

PubMed1993

E-cadherin: a differentiation marker in thyroid malignancies.

Loss of E-cadherin (uvomorulin), a Ca(2+)-dependent cell adhesion molecule required for normal epithelial function, has been attributed a pathogenetic role in tumor invasion. The expression of E-cadherin was studied in normal and neoplastic follicular epithelium of the human thyroid by Northern blot analysis and immunofluorescence on frozen tissue sections. In the normal thyroid (n = 10) and in benign thyroid disorders (n = 21; toxic diffuse goitre; multinodular goitre; follicular adenomas), E-cadherin mRNA levels were equally high and the follicles were generally stained, mainly along the lateral surface of the epithelial cells, by the anti-E-cadherin monoclonal antibody. In anaplastic thyroid carcinomas (n = 6) E-cadherin expression was very low or lacking. In papillary carcinomas (n = 23), E-cadherin mRNA levels varied from nearly normal to highly reduced, which roughly correlated with the overall immunofluorescence intensity. However, the immunostaining also revealed a heterogeneous "all-or-nothing" expression of E-cadherin among adjacent cells in the same tumor. In the follicular carcinomas (n = 9), E-cadherin mRNA levels were in general rather high but the immunostaining varied considerably. A few papillary and follicular tumors lacked immunoreactive E-cadherin in spite of high mRNA levels. In oxyphilic (Hürthle) cell tumors, comprising both adenomas (n = 4) and carcinomas (n = 2), E-cadherin immunoreactivity was reduced and distributed intracellularly rather than at the cell surface. The expression of E-cadherin in relapsing thyroid carcinomas and in tumors with metastatic spreading was, irrespective of the histiotype, low or lacking. Sequential Northern analysis revealed a close correlation between the expression levels of E-cadherin and the thyrotropin receptor. Together, the data suggest that in human thyroid malignancies both gene expression and posttranscriptional control of E-cadherin may be impaired.

Adenoma↗

PubMed1992

Structural and functional aspects of the thyroid follicular epithelium.

The thyroid epithelium is morphologically and functionally polarized, with an apical surface facing the follicular lumen containing colloid and a basolateral surface facing the interstitium. Iodination and thyroid hormone synthesis occur in the colloid at the apical plasma membrane. The introduction by Mauchamp et al. of primary cultures of porcine thyroid cells grown as a polarized, confluent monolayer on a filter in a bicameral chamber system has now made it possible to study in more detail the barrier function and vectorial ion transport in the thyroid epithelium. The follicular cells form a very tight monolayer (transepithelial resistance > 6000 ohm cm2) and establish a transepithelial potential difference (apical medium negative) of about 20 mV. These parameters are rapidly influenced by TSH, mainly by an action on apical sodium channels, and by EGF. The integrity of the barrier is, as in other epithelia, dependent on extracellular calcium. A calcium-dependent cell adhesion molecule, uvomorulin, is expressed at the lateral plasma membrane surface. EGF induces cell proliferation as well as migration of some of the epithelial cells to a position below the monolayer, which however maintains its polarity and barrier function. In contrast, during TPA-induced proliferation the barrier function is disrupted. Iodide is vectorially transported in basoapical direction while the epithelial layer is virtually impermeable for iodide transfer in the opposite direction. Iodide is concentrated in the cell by the basolateral "iodide-pump" and its efflux across the apical plasma membrane is rapidly and selectively increased by TSH via cAMP. EGF inhibits vectorial basoapical iodide transport mainly by reducing the iodide permeability of the apical plasma membrane. Together, these recent observations indicate that the ion content of the follicular lumen is strictly controlled by the thyroid epithelium.

Animals↗

PubMed1992

Polarized efflux of iodide in porcine thyrocytes occurs via a cAMP-regulated iodide channel in the apical plasma membrane.

The intracellular regulation of thyrotropin-stimulated iodide efflux was studied in polarized porcine thyrocytes grown as a continuous, tight monolayer in bicameral culture chambers. From a previous study using this system we know that thyrotropin rapidly increases iodide efflux in the apical but not basal direction of the polarized epithelium. [125I]-iodide efflux in apical direction was stimulated by thyrotropin in a concentration-dependent manner (1-10 U/l), whereas efflux in basal direction was unchanged at any thyrotropin dose. Thyrotropin-induced elevation of intracellular cAMP showed a corresponding concentration dependence. The selective stimulation of apical efflux by thyrotropin was evident also when re-uptake of iodide released in basal direction was blocked by perchlorate. The effect of thyrotropin on apical efflux was mimicked by 8-bromo-cAMP and forskolin, whereas agents known to activate the Ca2+/phosphatidylinositol cascade (epidermal growth factor) and protein kinase C (phorbol ester) or increase cytosolic [Ca2+] (A23187) were inactive. We conclude that the selective stimulation by thyrotropin of apical iodide efflux, corresponding to efflux in luminal direction in intact follicles, occurs via cAMP-regulated iodide channels present in the apical domain of the plasma membrane.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1992

A morphometric and biomechanic comparison of titanium implants inserted in rabbit cortical and cancellous bone.

The removal torques for screw-shaped pure titanium implants inserted in rabbit tibia and the femoral part of the knee joint and the tissue response to these implants, as quantitated with light microscopic morphometry on ground sections, were compared after 6 weeks, 3 months, and 6 months. The bone surrounding the femoral intra-articular implants was mostly cancellous, while cortical bone was formed around the tibial implants. The torque needed to remove the intra-articular implants increased with time, but there was no such increase for the tibial implants. At 6 weeks, significantly less torque was needed to remove the intra-articular implants in spite of the fact that significantly more bone was found in the threads of these implants as compared with the tibial implants. When calculating the amount of bone in threads situated in the cortical and subchondral passage, more was found in the threads of the tibial implants, which corresponded to the higher removal torque. Additional light microscopic observations on implants unscrewed after 12 months in rabbit tibia indicated that rupture occurred between the implant surface and calcified bone. Findings indicate that the resistance to unscrewing is dependent on the amount of compact bone surrounding a titanium implant.

Animals↗

PubMed1991

Non-polarized cell surface expression of HLA-A,B,C and HLA-DR antigens in Graves' thyroid follicle cells.

The intrathyroidal distribution and cell surface location of HLA-A,B,C and HLA-DR antigens was studied in polarized thyroid follicle cells from Graves' (n = 11) and normal (n = 3) thyroid tissue, using light and electron microscopy. Cryosections and isolated, open follicle segments were incubated with monoclonal antibodies against HLA-A,B,C and HLA-DR antigens and with patient sera containing autoantibodies against the microsomal antigen/thyroperoxidase. Immunoreactivity for HLA-A,B,C and HLA-DR on isolated thyroid follicle cells was frequently detected in Graves' disease, but absent in normal glands. There was a large variation in the immunolabelling between follicles as well as between different glands. Both HLA-A,B,C and HLA-DR immunoreactivity were detected on the apical and the basal surface of the follicle cells. Microsomal antigen/thyroperoxidase immunoreactivity was restricted to the apical cell surface. In contrast to normal tissue, HLA-DR positive cells with a dendritic or macrophage-like morphology were frequent in Graves' tissue. These cells adhered directly to the basal surface of isolated follicle segments. We conclude that HLA antigens are, unlike thyroid-specific plasma membrane constituents, expressed in a non-polarized manner at the surface of the follicular epithelium. These observations might have implications on the immune recognition of thyroidal autoantigens in Graves' disease.

Adult↗