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C Penel

Publications and source records attributed to C Penel.

At least 37 records · Page 2Linked to original sources
PubMed1994

Binding of plant isoperoxidases to pectin in the presence of calcium.

Some of the isoperoxidases present in an extract from zucchini hypocotyls--one anionic and two cationic--exhibited a Ca(2+)-dependent pelletability which resulted from an interaction with pectins. Endogenous pectins could be replaced by polygalacturonic acid or pectin extracted from citrus, but not by highly esterified pectin. The interaction between the isoperoxidases and the polysaccharides has been studied by centrifugation, by gel filtration, and with pectins attached in wells of a microtitration plate. These various binding tests have shown that the isoperoxidases had an affinity for the pectins in their Ca(2+)-induced conformation.

Calcium↗
PubMed1994

Thyrotropin regulation of basolateral Cl- and I- effluxes in thyroid follicles in culture.

This report describes chloride and iodide effluxes across the basolateral membrane of porcine thyroid follicles reconstituted in culture. Basolateral chloride efflux is activated by thyrotropin (TSH). TSH (10 mU/ml) induces a twofold increase in the initial rate of chloride efflux. Forskolin (FSK, 5 microM) which increases intracellular cAMP also stimulates the initial rate of chloride efflux 3.5-fold, whereas an increase in the free cytosolic Ca2+ with the ionophore A23187 or thapsigargin, fails to mimic the TSH effect. The chloride channel blocker 5-nitro-2(3-phenylpropylamino)benzoic acid (NPPB) dose dependently inhibits chloride efflux rates with the maximal and half maximal effects observed for 100 microM and 30 microM, respectively. Basolateral chloride efflux rates are also inhibited in the presence of the organic anion transporter blocker probenecid (5 mM) or the Cl-/HCO3- exchanger blocker 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS, 250 microM), respectively, by 60% and 40%, whereas it is not affected by ClO4 (100 microM). The initial rate of iodide efflux is weakly activated (1.4-fold) by TSH (10 mU/ml). TSH effect could be reproduced by agents known to activate Ca(2+)-dependent processes as A23187, ionomycin (1 microM), phorbol 12-myristate 13-acetate (TPA, 0.1 microM) and epidermal growth factor (EGF, 0.1 microM) which increase the initial rate of iodide efflux from 1.2- to 1.8-fold, whereas FSK is without effect. The chloride channel blocker NPPB (500 microM) is required to significantly inhibit the initial rate of iodide efflux by 30%. The initial rate of iodide efflux is also reduced by 30% in the presence of SITS (250 microM) or probenecid (5 mM) whereas it is activated by ClO4 (100 microM). We conclude that basolateral chloride and iodide effluxes are both regulated by TSH, using two different transduction pathways. Chloride efflux regulation may involve a cAMP transduction signal, whereas the regulation of iodide efflux may involve a Ca2+ signal. Furthermore, as the sensitivities of chloride and iodide effluxes for the anion transporter blockers (especially NPPB) are different, it seems likely that chloride and iodide use two different transport pathways.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1993

Cytological indication of the involvement of calcium and calcium-related proteins in the early responses of Bryonia dioica to mechanical stimulus.

The distribution of membrane-bound calcium, activated calmodulin, and callose synthesis was visualized in Bryonia dioica internodes before and after mechanical stimulus, using fluorescent probes, respectively, chlorotetracycline, fluphenazine, and aniline blue. Bright chlorotetracycline fluorescence remains localized in the plasma membrane of control cells, 30 s after stimulation calcium left the plasmalemma. A delocalization of activated calmodulin was observed after wounding and deposition of callose, which could not be detected before, appeared in the same times in most cells. The callose formation and the decrease in membrane-associated calcium suggest a rapid influx of calcium in the cytosol and an intervention of this ion in the cascade of the early events underlying Bryonia dioica thigmomorphogenesis.

Calcium↗
PubMed1993

Glycosylation of human prolactin regulates hormone bioactivity and metabolic clearance.

To analyze the role of individual glycosylation pattern on PRL biopotency, monomeric prolactin (PRL), secreted by human prolactinoma cells in culture, was isolated by gel filtration and separated by affinity chromatography on Concanavalin A-Sepharose or Lentil-Agarose. These lectins allowed the isolation of PRL glycoforms containing either biantennary, mannose-rich or fucosylated complex carbohydrate structures, respectively. Endoglycosidase treatment and carbohydrate content of PRL was found to be consistent with N-linked oligosaccharides of mannose-rich structure and complex units terminated in sialic acid. Mannose-rich PRL and PRL with biantennary oligosaccharides promoted cell growth of rat lymphoma cells to a diminished extent compared to non-glycosylated PRL (NG-PRL), indicating that the two major types of carbohydrate structure are able to decrease the intrinsic bioactivity of PRL. Metabolic clearance of the various forms of PRL in rats was also found to be highly dependent upon hormone glycosylation. The various glycosylated forms (G-PRLs) proved to be totally eliminated from the circulation within 60 min, faster than NG-PRL 10% of which was still present at that time. Mannose-rich or biantennary G-PRLs were differently cleared in a biphasial fashion with a similar rapid phase of about 2 min followed by distinct slow phases of 12 and 27 min, respectively. The presence of fucose did not alter this distribution. In contrast, NG-PRL was eliminated with a half-time of approximately 5 min, followed by a very slow disappearance over several h. It thus appeared that glycosylation increased the metabolic clearance rate of PRL from 0.13 +/- 0.07 ml/min for NG-PRL to 0.47 +/- 0.12 ml/min for PRL with biantennary carbohydrate chains and 0.8 +/- 0.2 ml/min for the hormone with mannose-rich oligosaccharides. The distribution of PRL to target and elimination organs was also found to be different according to the carbohydrate structure present in the hormone. NG-PRL and mannose-rich G-PRL showed higher incorporation in liver than biantennary G-PRL which was preferentially eliminated by the kidney. Altogether, the current data show that addition of oligosaccharides to PRL as well as carbohydrate structure contribute to modulate both the duration of the hormone in the blood and its distribution to different organs. It is proposed that glycosylation may selectively down-regulate PRL action at individual target tissues.

Animals↗
PubMed1993

In vitro slow fluctuation in horseradish peroxidase activity.

In vitro slow fluctuations in the level of horseradish peroxidase activity were observed in long-range experiments (72-144 h). Besides random fluctuations, regular slow oscillatory patterns with period lengths ranging from 10.0 to 39.0 h were detected by statistical analysis. The possibility that these oscillations in enzyme activity could have reflected changes in the physical environment of the experimental setup has been thoroughly examined and ruled out. Periodic exposition of the enzyme solution, otherwise kept in darkness, to blue light illumination was shown to influence the period of the oscillations. The changes in enzyme activity were correlated with a modification of the Michaelis constant estimated using guaiacol as substrate. This result was confirmed by the action of chemical modifiers of the enzyme, such as ferulic acid and rutin. It is thought that the observed oscillations in horseradish peroxidase activity are due to spontaneous and specific changes in the tridimensional structure of the enzyme in the thermic reservoir.

Circadian Rhythm↗
PubMed1992

Spatial and temporal thyrocyte response to TSH: a computer-assisted image analysis.

Pseudopods at the apical pole of porcine thyroid monolayers in culture were considered as reflecting individual thyrocyte responses to thyrotropin (TSH) stimulation. Scanning electron microscopy and computer-assisted image analysis showed that whatever TSH stimulation was used, the pseudopods were characterized by two populations: P1 with small diameters (2 microns) and P2 with greater diameters (5 microns). The density of P1 rapidly increased to reach a plateau, while P2 continuously increased during stimulation. Two-dimensional pseudopod patterns were compared with random point distributions by means of two topographical parameters: the interpseudopod distances and angles. A factorial analysis of experimental distribution of pseudopods obtained after increasing stimulation times displayed a shift from a nonrandom (10-20 min) to a random (60-90 min) distribution. Clusters of three pseudopods characterized by short distances (6-9 microns) and equilateral organization (angles 40-60 degrees) were observed after a 10-min stimulation. These results suggested that early thyrocyte response to TSH stimulation is characterized by interrelations between three adjoining cells, with the thyrocyte response later appearing as random.

Animals↗
PubMed1989

The thyroid cell monolayer in culture. A tight sodium absorbing epithelium.

When cultured on collagen coated nitrocellulose filters, thyroid epithelial cells form morphologically and functionally polarized monolayers. The bioelectric parameters of these monolayers were measured after mounting in Ussing chambers; transepithelial potential (Vab), short circuit current (Isc) and transepithelial resistance were respectively 12 +/- 1 mV (apical side negative), 3.8 +/- 0.2 microA cm-2 and 3250 +/- 214 omega cm2 (mean +/- SEM, n = 75). Eighty two percent of the short circuit current was related to sodium absorption as shown by inhibition by apical amiloride (Km = 0.2 microM) and by basal ouabain (K1/2 = 0.3 microM). Amphotericin B (5-25 micrograms/ml) added to the apical bath increased Isc suggesting an apical rate-limiting step. Step by step replacement of choline by Na+ in a Na+-free medium resulted in a progressive increase in Vab and Isc with half maximal effect at 20 +/- 1 mM Na+. Thyrotropin (TSH) increased Isc and Vab in a biphasic way with a transient maximum after 5 min and a plateau after 20 min (about four times the basal level at 100 microU/ml TSH). This increase in sodium transport was also inhibited by apical amiloride. Thus, in culture, the thyroid cell monolayer behaves as a tight sodium absorbing epithelium controlled by TSH, with a rate limiting apical sodium channel as the entry mechanism and a basolateral Na+, K+-ATPase as the electromotive force.

Amiloride↗
PubMed1989

Down regulation of hypertrophied follicular cell volume in thyroid hyperplastic gland.

In the present study, changes in thyroid follicular cell volume and its regulation have been investigated during the early involution of a hyperplastic goitre. Male Wistar rats were administered an iodine deficient diet for 6 months with propylthiouracil (PTU, 0.15%) during the last two months. At the end of iodine deficiency (day 0), some rats were killed and the others received a normal iodine diet. These rats were killed after different periods of iodine refeeding. Thyroid follicular cell volume was very high in hyperplastic gland whereas thyroid protein concentration was low. Thyroid follicular cell volume quickly decreased when rats were normally iodine refed, whereas thyroid protein concentration increased. Electron microscopal observations showed that thyroid follicular cells retained their endocrine aspect in hyperplastic state and throughout the iodine refeeding period. Using concomitant stereological and biochemical techniques, it is shown that the amount of cellular iodide and an unknown iodinated compound strongly increased during the early iodine refeeding. Plasma TSH was high on day 0 and remained at this level until day 8 whereas plasma T3 and T4 were low on day 0 and remained at this low level until day 4. The present data show that the involution of thyroid follicular cell volume is induced by iodide and mediated by an iodinated compound at least in the initial phase, and is independent of plasma TSH, T3, T4, so indicating the involvement of a thyroid autoregulatory mechanism. These changes in cell volume may be of importance in ion transport, i.e. in the metabolism of thyroid follicular cell during the early involution of the hyperplastic goitre.

Animals↗
PubMed1987

Involution of hyperplastic goitre in the adult male rat. Tissue compartment process with early iodide effect: a stereological and biochemical study.

The morphological and functional changes during involution of hyperplastic goitre have been investigated in the adult male rat. Male wistar rats received an iodine-deficient diet for 6 months and during the last 2 months received propylthiouracil (PTU, 0.15%). By the end of this treatment (day 0), a hyperplastic goitre was obtained. A normal iodine supply was then given and PTU withdrawn. During the first 8 days of iodine refeeding, the plasma thyrotropin (TSH) remained at a high level (ten times the control value), whereas the thyroid iodide content was low on day 0, markedly increased on day 1 and decreased on day 4. Plasma T3 and T4 levels remained unchanged for 4 days and only increased on day 8. The total thyroid protein concentration was low on day 0 and then increased rapidly on day 8 (by 34%). The volume density of colloid remained low and unchanged until day 8, when it started to increase. However, the thyroid epithelial cell volume and the volume density of capillaries were raised on day 0, decreased rapidly in the next 8 days and more slowly later on. The total number of thyroid epithelial cells was considerably raised in the hyperplastic gland. It did not vary until day 16, when it decreased slowly, reaching a plateau on day 45 above the control value. The present data show that involution of hyperplastic goitre in the rat is due essentially to a decrease in thyroid epithelial cell volume and to a reduction of the increased number of capillary blood vessels present. The decrease in the number of epithelial cells is only 16.5%, suggesting that the death of thyroid epithelial cells contributes little. Half the process of involution, which occurs from days 0 to 8, is controlled by the thyroid iodide concentration rather than TSH, indicating the involvement of a thyroid autoregulatory mechanism. It must be emphasized, however, that the discontinuous pattern of epithelial cell number during involution may indicate that some cells with larger nuclei and more rapid turnover disappear more quickly after iodine refeeding.

Animals↗
PubMed1987

Thyroid autoregulation: impact on thyroid structure and function in rats.

Global response of the thyroid to a 10-fold increase in plasma iodide concentration results only in modifications of basolateral transfer for iodide where, by a balance phenomenon between influx and efflux, a net thyroid intake of 1.2 micrograms I/day is constantly maintained. The other main steps of thyroid iodine metabolism, thyroglobulin (Tg) iodination, endocytosis, and hydrolysis, remain constant. A stationary hormone secretion delivery results. This constant state is not found at a cellular level, where structural changes are observed in correlation with functional regulation of the cell dynamic state. Thus, an increase in plasma iodide concentration results in an increase of the apical membrane area (40%), whereas the basolateral membrane area decreases (18%). The volume of the follicle lumen increases (76%). Nevertheless, neither epithelial cell volume nor the structure of microvilli are modified. Comparison of iodine fluxes through the apical and basolateral membrane of the epithelial cell shows that an increase in plasma iodide concentration is correlated to a decrease of the Tg iodination and endocytotic fluxes (45%). A regulation also appears for basolateral transfer of iodide, whereas the lysosome system does not modulate the hormone secretion mechanism.

Animals↗
PubMed1987

Epithelial cell polarization in culture: orientation of cell polarity and expression of specific functions, studied with cultured thyroid cells.

Isolated porcine thyroid cells reorganize in culture into various types of multicellular structure, which differ in the orientation of cell polarity and in the surface of the cell layer accessible to molecules present in the culture medium. The types of structure are: (1) follicles: the basal pole is oriented toward the medium; (2) inside-out follicles or monolayers: the apical pole is facing the culture medium; (3) monolayers on a permeable substratum: both sides of the cell layer are accessible to the medium. Follicles can be transformed into inside-out follicles or monolayers and vice versa by manipulation of the external cell environment and without dissociating the cells. Cells concentrate iodide and respond to acute stimulation by thyroid-stimulating hormone (TSH) when the basal pole is accessible, and organification occurs only when cells form a closed follicular lumen. In porous-bottomed culture chambers monolayers are formed with the basal surface accessible to the medium and the apical compartment separated from the medium. Under these conditions 85-95% of the thyroglobulin produced is secreted apically and 5-15% basally. Thyrotropin stimulates (X3) apical accumulation without modifying secretion in the basal compartment. Sodium transport across the cell layer has been characterized. An amiloride-sensitive influx occurs at the apical pole whereas the Na+/K+-ATPase, localized in the basolateral membrane, mediates ouabain-sensitive efflux at the basal pole. The thyroid epithelium in culture appears therefore as a Na+-absorbing epithelium. The role of this transport in the stabilization of cell polarity is discussed.

Animals↗
PubMed1987

Polarized properties of thyroid cells: a study with cultured porcine cells.

In primary culture porcine cells form polarized cell layers. We have designed culture conditions in which we can have access to only one side of the cell layer, either the apical or the basal surface. In addition, using culture chambers with permeable bottom we can have access to either side of the cell layer which separates two compartments. Using these organized systems we have shown that the iodide concentrating mechanism and the TSH-receptor adenyl cyclase complex are localized on the basolateral domain of the thyroid cell plasma membrane. We also demonstrated the existence on the apical surface of an amiloride sensitive sodium uptake. Finally we observed that about 10% of newly synthesized thyroglobulin appears to be secreted directly into the basal compartment, 90% being secreted in the apical compartment.

Adenylyl Cyclases↗
PubMed1987

Cell kinetics of thyroid epithelial cells during hyperplastic goitre involution.

Thyroid epithelial cell kinetics were investigated in rats when a normal iodine diet was re-established after a long period of iodine deficiency supplemented with propylthiouracil (0.15%) for the last 2 months. In the first (prelabelling) experiment, all rats were labelled with a single injection of [3H]thymidine 2 days before iodine refeeding in order to follow the fate of the prelabelled cells. In the second experiment, the pulse-labelling index at the time of killing was measured; for this purpose the rats received [3H]thymidine 1 h before death. In these two experiments autoradiography was performed on histological sections. Thyroids were excised on day 0 and then at various intervals up to day 73 of iodine refeeding. Plasma tri-iodothyronine (T3) and thyroxine (T4) were very low until day 4 and then increased to reach control values on day 30. Thyroid concentration of iodide rose to 20 times the value on day 0, remained at this high level until day 2, and then diminished on day 4 to reach the control value on day 16. Plasma TSH concentrations were very high in iodine-deficient rats and did not vary significantly until day 8, when they fell rapidly to reach the control value on day 30. Thyroid weight, raised on day 0, decreased relatively quickly until day 4, then more slowly until day 30. Total thyroid epithelial cell number, high on day 0 (30.7 x 10(6) cells) was constant until day 16, then decreased until day 30 at which time a plateau was reached.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Isolation of highly purified fractions of plasma membrane and tonoplast from the same homogenate of soybean hypocotyls by free-flow electrophoresis.

A procedure is described whereby highly purified fractions of plasma membrane and tonoplast were isolated from hypocotyls of dark-grown soybean (Glycine max L. var Wayne) by the technique of preparative free-flow electrophoresis. Fractions migrating the slowest toward the anode were enriched in thick (10 nanometers) membranes identified as plasma membranes based on ability to bind N-1-naphthylphthalamic acid (NPA), glucan synthetase-II, and K(+)-stimulated, vanadate-inhibited Mg(2+) ATPase, reaction with phosphotungstic acid at low pH on electron microscope sections, and morphological evaluations. Fractions migrating farthest toward the anode (farthest from the point of sample injection) were enriched in membrane vesicles with thick (7-9 nanometers) membranes that did not stain with phosphotungstic acid at low pH, contained a nitrate-inhibited, Cl-stimulated ATPase and had the in situ morphological characteristics of tonoplast including the presence of flocculent contents. These vesicles neither bound NPA nor contained levels of glucan synthetase II above background. Other membranous cell components such as dictyosomes (fucosyltransferase, latent nucleosidediphosphate phosphatase), endoplasmic reticulum vesicles (NADH- and NADPH- cytochrome c reductase), mitochondria (succinate-2(p-indophenyl)-3-p-nitrophenyl)-5-phenyl tetrazolium-reductase and cytochrome oxidase) and plastids (carotenoids and monogalactosyl diglyceride synthetase) were identified on the basis of appropriate marker constituents and, except for plastid thylakoids, had thin (<7 nanometers) membranes. They were located in the fractions intermediate between plasma membrane and tonoplast after free-flow electrophoretic separation and did not contaminate either the plasma membrane or the tonoplast fraction as determined from marker activities. From electron microscope morphometry (using both membrane measurements and staining with phosphotungstic acid at low pH) and analysis of marker enzymes, both plasma membrane and tonoplast fractions were estimated to be about 90% pure. Neither fraction appeared to be contaminated by the other by more than 3%.

Journal Article↗
PubMed1986

Negative effect of iodide on the survival of newly divided epithelial cells in chronically stimulated rat thyroid.

The aim of this work was to investigate some aspects of the thyroid epithelial cell kinetics during the iodide-induced involution of a hyperplastic goitre in the rat. Rats were made iodine-deficient for 6 months, and propylthiouracil (PTU) (0.15%) was added to the diet during the last 2 months. Thereafter, rats were refed with iodide and PTU was removed (day 0). Forty-eight hours previously, all the rats were injected with tritiated thymidine ([3H]TdR) (1 microCi/g). Some animals were killed 1 hr or 24 hr after [3H]TdR injection (i.e. on day -2 and -1, day 0 corresponding to the restoration of a normal iodine diet); the other animals were killed after different delay periods and following [3H]TdR injection. Autoradiography of thyroid sections, iodine determination of plasma iodide and protein-bound iodine (PBI), and RIA of plasma thyroid stimulatory hormone (TSH) were performed. Plasma TSH concentration was very high on day 0 of iodide refeeding (3000 +/- 330 ng/ml) and remained at this level until day 8. Plasma PBI was very low on day 0, remained so until day 4 and greatly increased on day 8. Plasma iodide was also very low on day 0, but markedly increased on day 1, then did not vary significantly until day 43 of iodine refeeding. Thyroid weight, elevated on day 0, decreased relatively quickly until day 30, then more slowly until day 73. The [3H]TdR labelling index (LI) of the thyroid epithelial cells (TEC) was high on day 0 (56 +/- 3 labelled cells/10,000 cells), and 24 hr thereafter increased to 104 +/- 3, by division of the labelled cells. On day 1 of iodine refeeding, the LI had abruptly decreased to about half this value and then remained stable for 3 more days. Between day 4 and day 16, a progressive decline in the LI, (by about 3-4 per day), was observed. The LI showed no further modification, up to day 73, the longest period investigated. The decrease in LI occurred without any significant changes in the labelling intensity (grain count) of the remaining labelled cells between day 1 and 16, this indicates that no cell division took place during this period. The data are therefore interpreted as showing a biphasic elimination after iodide refeeding, of cells that were actively proliferating during the goitrous state.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

[Possible regulation of the growth of thyroid tissue by plasma iodide].

Rats on iodine deficient diet for 6 months received propylthiouracil (PTU) (0.15%) during the last 2 months. At the end of this treatment, PTU was withdrawn and the rats were iodine refed. 48 hrs. before the iodine refeeding all rats were injected with 3H thymidine. The results showed that some prelabelled cells in the hyperplastic goitre preferentially disappeared during its involution and therefore are more sensitive to iodine.

Animals↗