Search PubMed⌕ Search

Biomedical subjects

J Crabbé

Publications and source records attributed to J Crabbé.

At least 19 recordsLinked to original sources
PubMed1998

Late development of resistance to bromocriptine in a patient with macroprolactinoma.

We report the case of a man with an invasive macroprolactinoma who developed resistance to bromocriptine to which he had previously responded satisfactorily for 5 years. Subsequently, hyperprolactinemia was controlled equally well with 600 microg quinagolide daily and later with 4.5 mg cabergoline weekly. This observation suggests that a loss of dopamine receptors at the tumoral cell surface might be the mechanism underlying acquired resistance to bromocriptine. In addition, no tumor growth was observed over a 10-year follow-up, which virtually excludes a malignant transformation of the prolactinoma. This case emphasizes the need for close supervision of patients with macroprolactinoma, even after the serum prolactin concentration has been normalized by bromocriptine. It furthermore illustrates the usefulness of quinagolide and cabergoline when resistance to bromocriptine develops after a prolonged period of adequate response to this drug.

Aminoquinolines↗
PubMed1996

Effects of corticosteroids on parameters related to Na+ transport by amphibian renal distal cells (A6) in culture.

The present study addresses the effects of the hormones aldosterone and corticosterone, as well as those of dexamethasone, on cultured renal amphibian cells, focusing on parameters thought relevant for the further understanding of the regulation by these steroids of Na+ reabsorption along the renal tubule. Exposure to these steroids of A6 cell monolayers grown on a permeable support produced a motor, dose-dependent, increase in Na+ transport, reflected by the short-circuit current, Isc. (Na+ + K+)-ATPase activity and ouabain binding, both of which are linearly correlated with Isc in control tissue, also increased significantly after steroid treatment. Dexamethasone was consistently more active than corticosterone and aldosterone on the parameters studied. The increase in Isc and (Na+ + K+)-ATPase activity elicited by dexamethasone could be blocked by the glucocorticoid antagonist RU 486, whereas it was only slightly reduced by the mineralocorticoid antagonist, spironolactone. In contrast, the latter strikingly reduced the effects of aldosterone on these parameters, unlike RU 486. Furthermore, the effects of large doses of dexamethasone and aldosterone combined were not additive. Taken together, the data presented appear compatible with the view that the effects of aldosterone on Na+ transport by A6 cells are mediated by a fraction of the receptors involved in the response to dexamethasone; they furthermore raise the question of whether, in lower vertebrates, it is relevant to make a distinction between "gluco" and "mineralo"corticoids.

Adrenal Cortex Hormones↗
PubMed1996

Effects of dexamethasone on (Na+ + K+)-ATPase and other parameters related to transepithelial Na+ transport by amphibian renal distal cells (A6) in culture.

In the present report, the effects exerted by dexamethasone on transepithelial, electrogenic Na+ transport across A6 cell monolayers grown on permeable support were further characterized in terms of time course and relationship to the rate of Na+ transport; furthermore this agonist was compared to vasopressin and insulin. (Na+ + K+)-ATPase activity and density of ouabain binding sites were measured in cell homogenates and on dispersed cells, respectively, after documenting transepithelial electrical parameters of the preparations. Na+ transport, measured by short-circuit current (Isc), was increased almost five-fold (control: 6.7 +/- 0.1 microA/cm2) after incubation with 10(-7) M dexamethasone for 24 h. Stimulation of Na+ transport rate was associated with a 2.3-fold increase in (Na+ + K+)-ATPase activity (control: 5.5 +/- 0.3 micromol Pi/mg prot.h), and ouabain binding site density almost doubled (control: 236 +/- 10 fmol/10(6) cells). The steroid acted on the Na+ pump of A6 cells in the absence of transepithelial Na+ transport, with intracellular Na+ ion activity playing an additional role in terms of cell Na+ pump numbers. In the case of insulin and vasopressin, in contrast, there was no effect on Na+ pump activity in the absence of Na+ transport by A6 cell monolayers. The increase in (Na+ + K+)-ATPase activity observed in A6 cell monolayers treated with dexamethasone is therefore a result of the direct induction of Na+ pump biosynthesis, with an almost proportional insertion of operational Na+ pumps into the basolateral membrane. In contrast, increased Na+ entry at the apical cell pole appears to be essential for insulin and vasopressin action on A6 cell Na+ pump.

Animals↗
PubMed1995

Aldosterone interaction on sodium transport and chloride permeability: influence of epithelial structure.

The effects of aldosterone on sodium transport and chloride permeability were investigated by electrophysiology in two structurally distinct epithelial used as models for the distal renal tubule: the A6 cell monolayer as compared with the amphibian skin epithelium (ASE). Short-circuit current (Isc) and transepithelial conductance (Gt) were measured in A6 monolayers incubated overnight with(out) aldosterone. Cell and shunt conductances (Gcell and Gsh) were also determined, as well as the conductive nature of the chloride pathway. These parameters were correlated with sodium and chloride fluxes in A6 cells (JNa and JCl) and compared with the data recorded across ASE (Bufo marinus). The existence of a cAMP-dependent chloride secretory pathway in A6 cells was also investigated upon exposition to arginine vasopressin (AVP) or oxytocin. When A6 monolayers were incubated with aldosterone, Gt significantly increased with respect to control preparations; this increase resulted solely from an increase in Gcell, and was reflected by a 3-fold increase in Isc. There was a significant relationship between Isc and Gcell, as well as between Isc and JNa in both control and aldosterone-stimulated preparations. The A6 clone used was devoid of cAMP-dependent chloride secretory activity and was unresponsive to AVP or oxytocin. Thus, comparison between ASE and A6 preparations revealed two major differences: unlike ASE, (i) aldosterone has no effect on Gsh and (ii) no conductive reabsorptive chloride pathway is operative in A6 monolayers tested. In addition, cobalt had no effect on electrical parameters of A6 monolayers. These observations show that difference in epithelial structure is reflected in terms of electrophysiological response to aldosterone, which suggests that cell heterogeneity could be a prerequisite for observing a conductive reabsorptive chloride pathway in aldosterone-responsive, sodium-transporting epithelia.

Aldosterone↗
PubMed1994

Subtypes of Madin-Darby canine kidney (MDCK) cells defined by immunocytochemistry: further evidence for properties of renal collecting duct cells.

The Madin-Darby canine kidney (MDCK) cell line has been proposed as a model for studying intercalated (IC) cells of the renal cortical collecting duct. The IC cells are characterized by peanut lectin (PNA) binding capacity, carbonic anhydrase (CA) activity and Cl(-)-HCO3- exchange mediated by a band 3-related protein. It has been suggested that these properties are also expressed in MDCK cells. So far however, the nature of the specific protein involved in Cl(-)-HCO3- exchange, the type of CA isozyme and the relationship between these two characteristics and PNA binding, have not been investigated in MDCK cells by immunocytochemical methods. Using two antibodies raised against human erythrocyte band 3 protein and two against human erythrocyte CA I and II isozymes, our study provides evidence that a protein related to band 3 is expressed in about 5% of cultured MDCK cells; these band 3-positive cells do not bind PNA and are not reactive for CAI or CAII. About 30% of the MDCK cells bind PNA, two-thirds of which are also CAII-positive. A majority (about 65%) of MDCK cells is not reactive for the three markers used; their density is increased after incubation with aldosterone. These data indicate (i) that the Cl(-)-HCO3- exchange of the MDCK cells could be related to human erythrocyte band 3, (ii) that the CA activity of the MDCK cell line bears antigenic identity with the erythrocyte CA II isozyme and (iii) that the latter is always co-localized with PNA binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Electron microprobe analysis of electrolytes in whole cultured epithelial cells.

Microprobe analysis was used to determine electrolyte contents in whole epithelial sheets of A6 cells and to investigate the most critical points of this method. Analysis of dextran standard sections of different thickness revealed that low accelerating voltages of about 10 kV are best suited for whole freeze-dried cells on thick supports, since 5 microM thick sections are not penetrated by 10 kV electrons. Washing of A6 cells for 10 sec with distilled water led to cell swelling of about 40%, but the molar concentration ratios and the concentrations per dry weight (dw) were not altered. Washing for 60 sec with distilled water caused a further increase in cell volume (120%) and loss of cellular K and Cl (90 mmol/kg dw). Washing with isotonic NH4- acetate led to a loss of cell Cl already after 10 sec. To characterize the Na transport compartment, A6 cells cultured on permeable supports were washed for 5 sec with distilled water, freeze-dried, and analyzed. Inhibition of transepithelial Na transport by ouabain increased Na/P from 0.15 +/- 0.07 to 0.75 +/- 0.03 and Cl/P from 0.21 +/- 0.001 to 0.38 +/- 0.003 while K/P decreased from 0.83 +/- 0.08 to 0.32 +/- 0.03. The changes in cell Na and K contents can be explained by K/Na exchange; the increase in Cl content indicates some cell swelling. Since the ouabain-induced changes could be prevented by apical amiloride, the apical membrane provides the most important pathway for Na entry in A6 cells.

Animals↗
PubMed1993

K+ recirculation in A6 cells at increased Na+ transport rates.

Homocellular regulation of K+ at increased transcellular Na+ transport implies an increase in K+ exit to match the intracellular K+ load. Increased K+ conductance, gK, was suggested to account for this gain. We tested whether such a mechanism is operational in A6 monolayers. Na+ transport was increased from 5.1 +/- 1.0 microA/cm2 to 20.7 +/- 1.3 microA/cm2 by preincubation with 0.1 mumol/l dexamethasone for 24 h. Basolateral K+ conductances were derived from transference numbers of K+, tK, and basolateral membrane conductances, gb, using conventional microelectrodes and circuit analysis with application of amiloride. Activation of Na+ transport induced an increase in gb from 0.333 +/- 0.067 mS/cm2 to 1.160 +/- 0.196 mS/cm2 and tK was reduced to 0.22 +/- 0.01 from a value of 0.70 +/- 0.05 in untreated control tissues. As a result, gK remained virtually unchanged at increased Na+ transport rates. The increase in gb after dexamethasone was due to activation of a conductive leak pathway presumably for Cl-. Increased K+ efflux, IK, was a consequence of the larger driving force for K+ exit due to depolarization at an elevated Na+ transport rate. The relationship between calculated K+ fluxes and Na+ transport rate, measured as the Isc, is described by the linear function IK = 0.624 x INa -0.079, which conforms with a stoichiometry 2:3 for the fluxes of K+ and Na+ in the Na+/K(+)-ATPase pathway. Our data show that homocellular regulation of K+ in A6 cells is not due to up-regulation of gK.

Amiloride↗
PubMed1993

Localization of a Band 3-related protein in the mitochondria-rich cells of amphibian skin epithelium.

Based on immunoblotting procedure, the isolated epithelium of amphibian skin was found to contain a 180 kDa protein which cross-reacts with a polyclonal antiserum raised against human erythrocyte Band 3. Immunoperoxidase and immunofluorescence staining techniques indicated that the Band 3-related protein was localized in the mitochondria-rich cells (MRC) of this epithelium, with characteristic apical labelling pattern. Our findings show that the putative apical anion exchanger of the MRC is immunologically related to the band 3 multigenic family, which catalyzes Cl(-)-HCO3- transmembranous exchange. It thus suggests a molecular basis for the role played by these cells in the transepithelial Cl- pathway and acid-base regulation.

Animals↗
PubMed1992

Osmotic swelling and membrane conductances in A6 cells.

Hyposmotic basolateral perturbations (-30 mosmol/kg) in cultured renal layers (A6) increased basolateral membrane conductance more than 2-fold within 10 min; the increase was partly due to upregulation of K+ conductance, but other conductive pathways were also activated. The raise in apical membrane amiloride-sensitive Na+ conductance was less pronounced; it appears to be due to secondary effects.

Animals↗
PubMed1992

Conductive chloride flux across amphibian skin: inhibition by indacrinone and cobalt ion.

When amphibian skin was incubated under conditions in which transepithelial sodium transport was abolished, a conductive transepithelial Cl- flux arose when Cl- was removed from one of the compartments. This flux was matched by short-circuit current and it accounted entirely for transepithelial conductance. Cl- influx was larger than efflux; it was linearly related to the magnitude of transepithelial Cl- concentration difference. When applied to the epithelial surface of the tissue, divalent metal cations such as Co2+, and the ethacrynic acid derivative, indacrinone, reduced rapidly and reversibly both transepithelial Cl- (in)flux and short-circuit current. Frog skin proved to be more sensitive to these inhibitors than toad skin. Further characterization of transepithelial Cl- pathway(s) should benefit from the fact that Cl- across amphibian skin can easily be monitored by the short-circuit current method, and from the availability of agents which inhibit this passive flux rapidly and reversibly.

Animals↗
PubMed1992

Basolateral membrane conductance in A6 cells: effect of high sodium transport rate.

Conductance of apical and basolateral membranes in short-circuited cultured renal distal cells (A6) was determined using microelectrodes. Epithelia were pre-incubated with 0.1 mumol/l dexamethasone in the presence of 4 mumol/l amiloride to prevent increase in apical Na+ entry. Omission of amiloride increased the Isc from 5.7 to 27.6 microA/cm2 due to the rise in apical membrane conductance from 21 to 595 microS/cm2. Apical fractional resistance decreased from 0.89 to 0.40 and cells depolarized from -52 to -4 mV. Basolateral membrane conductance, which was 320 microS/cm2 at partially inhibited transport, was not significantly altered during the first 2 min following establishment of high transport activity; it started to increase thereafter reaching a more than threefold higher value of 1324 microS/cm2 within 12 min. The gain cannot be explained by increase in partial K+ conductance. Disappearance of the conductance after reduction of basolateral Cl- or in the presence of the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)benzoate indicates a Cl- conductance, which appears to be activated by depolarization.

Amiloride↗
PubMed1992

Influence of apical Na+ entry on Na(+)-K(+)-ATPase in amphibian distal nephron cells in culture.

1. Transepithelial Na+ transport, Na(+)-K(+)-ATPase activity and ouabain binding were measured in cells originating from the distal part of amphibian nephron (A6) which form 'tight' monolayers in culture, under standard (control) incubation conditions and after various manoeuvres designed to reversibly interfere with Na+ transport. 2. At spontaneous transport rate, the short-circuit current (which reflects transepithelial Na+ transport) and the Na(+)-K(+)-ATPase activity averaged 7.0 microA/cm2 and 5.9 mumol Pi/(mg protein.h), respectively (n = 53). Short-circuit current and Na(+)-K(+)-ATPase activity appeared to be directly related over a wide range. 3. Suppression of Na+ transport led to a progressive decrease in Na(+)-K(+)-ATPase activity over several hours, with an apparent half-life of approximately 6 h after subtraction of baseline enzyme activity. 4. When A6 cells were allowed to resume sodium transport, the short-circuit current and Na(+)-K(+)-ATPase activity returned to control levels within 12-24 h, the former recovering somewhat faster. 5. When apical sodium concentration was reduced, a decrease in enzyme level occurred inasmuch as short-circuit current decreased. 6. There was good agreement between the measured enzyme activity and ouabain binding onto dispersed A6 cells, which suggests that it is unlikely that the changes observed result from internalization vs. insertion in the plasma membrane of sodium pumps.

Animals↗
PubMed1991

Voltage dependent membrane conductances in cultured renal distal cells.

Cultured Na(+)-transporting epithelia from amphibian renal distal tubule (A6) were impaled with microelectrodes and analyzed at short-circuit and after transepithelial voltage perturbation to evaluate the influence of voltage on apical and basolateral membrane conductances. For equivalent circuit analysis, amiloride was applied at each setting of transepithelial potential. At short-circuit, apical and basolateral membrane conductances averaged 88 and 497 microS/cm2, respectively (n = 10). Apical membrane conductance, essentially due to Na(+)-specific pathways, decreased after depolarization of the apical membrane. The drop was considerably larger than predicted by the Goldman-Hodgkin-Katz (GHK) constant-field equation. This suggests decrease in permeability of the apical Na+ channels upon depolarization. Basolateral membrane conductance, preferentially determined by K+ channels, increased after hyperpolarization of the basolateral membrane. This behavior is contrary to the prediction of the GHK constant field equation and reflects inward rectification of the K+ channels. The observed rectification patterns can be valuable for maintenance of cellular homeostasis.

Animals↗
PubMed1991

Aldosterone and chloride conductance of amphibian skin.

Chloride influx (JCl) across the skin of toads maintained in dilute MgCl2 or Na2SO4 was determined after overnight incubation with(out) aldosterone, and related to mitochondria-rich cell (MRC) density of the preparations. Adaptation to MgCl2 vs. Na2SO4 was reflected by higher plasma aldosterone in the former group (17 vs. 3 nmol/l, respectively) while JCl was lower, even after overnight incubation (172 vs. 318 pmol cm-2 s-1). Incubation with aldosterone induced a more pronounced increase in JCl in the case of Na2SO4- vs. MgCl2-adapted toads (delta JCl: 242 vs. 25 pmol cm-2 s-1, respectively), which could be related to difference in MRC density between these two groups (1078 vs. 615 cells/mm2, respectively). On the other hand, the in vitro effect of aldosterone on Na+ transport (assessed by Isc) was equally pronounced in both groups, and thus independent of MRC density. These data suggest that aldosterone, rather than being involved in MRC proliferation, stimulates Cl- conductance by influencing the functional state of MRC.

Aldosterone↗
PubMed1991

Effects of environmental conditions on mitochondrial-rich cell density and chloride transport in toad skin.

Chloride flux across amphibian skin is usually passive, yet largely conductive; previous reports have suggested that aldosterone influences this pathway. The conductive Cl- pathway and its regulation were examined further, across the abdominal skin of toads (Bufo marinus) adapted to various environments. Short-circuit current (Isc), total conductance (Gt) and Cl- influx (JCl) were measured in conditions such that there was net Cl- movement in absence of Na+ transport. In salt-deprived animals compared to salt-adapted ones, there was a significant increase in JCl (563 vs 200 pmol cm-2 s-1), aldosteronaemia (4.2 vs 1.1 nmol/l), as well as MRC density (1458 vs 851 mm-2). After adaptation to dilute Na2SO4 compared to MgCl2, JCl (631 vs 313 pmol cm-2 s-1) as well as the density of mitochondria-rich cells (MRC) (1306 vs 710 mm-2) practically doubled, while the toads' aldosteronaemia was lower (2.4 vs 10.8 mmol/l). In all groups of toads, JCl was matched by Isc, and there was a close correlation between Gt and JCl (r = 0.96), which confirms the conductive nature of transepithelial Cl- movement. Furthermore, the relationship between JCl and MRC density (r = 0.75) argues in favour of a role played by MRC on Cl- conductance of epithelial such as amphibian skin. As aldosterone injected for 1 week into NaCl-adapted toads did not influence MRC density and as aldosteronaemia was not correlated with Cl- conductance, this hormone does not emerge as the determinant of these parameters.

Aldosterone↗