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D Duval

Publications and source records attributed to D Duval.

At least 91 records · Page 5Linked to original sources
PubMed1982

Dexamethasone-induced inhibition of prostaglandin production dose not result from a direct action on phospholipase activities but is mediated through a steroid-inducible factor.

Investigations were carried out to define the mechanisms of steroid-induced inhibition of prostaglandin secretion by rat renomedullary cells in tissue culture. Although it was strongly proposed that glucocorticoids may inhibit phospholipase A2 activity, we present several pieces of evidence against a direct action of dexamethasone on phospholipase activities. First, dexamethasone, which significantly decreases the release of labeled material from cells prelabeled with [3H]arachidonate, does not significantly alter the pattern of distribution of the radioactivity among the various classes of cell lipids. In addition, direct measurement of phospholipase A3 activity in dexamethasone-treated cells failed to show any significant decrease in the deacylation capacity. On the other hand, several indications suggest that dexamethasone may induce the secretion of a non-dialysable, transferable factor able to inhibit prostaglandin production, the mechanism of which remains to be investigated.

Animals↗
PubMed1982

Preparation of a pure monoiodo derivative of the bee venom neurotoxin apamin and its binding properties to rat brain synaptosomes.

The preparation and purification of an active monoiodo derivative of apamin is described. Radiolabeled monoiodoapamin (2000 Ci/mmol) binds specifically to rat brain synaptosomes at 0 degrees C and pH 7.5 with a second order rate constant of association (ka = 2.6 x 10(7) M-1 s-1) and a first order rate constant of dissociation (kd = 3.8 x 10(-4) s-1). The maximal binding capacity is 12.5 fmol/mg of protein and the dissociation constant is 15-25 pM for the monoiodo derivative and 10 pM for the native toxin. The apamin receptor is destroyed by proteases suggesting that it is of a proteic nature. Neurotensin and its COOH-terminal partial sequences are the only molecules unrelated to apamin that are able to displace monoiodoapamin from its receptor at low concentrations. Half-displacement occurs at 170 nM neurotensin. This property is due to the presence in the COOH-terminal sequence of neurotensin of two contiguous arginine residues, a structure analogous to that of the apamin active site. The binding of monoiodoapamin to its receptor is sensitive to cations. Increasing K+ or Rb+ concentrations from 10 microM to 5 mM selectively enhances the binding by a factor of 1.8. Increasing the concentration of any cation from 1 to 100 mM completely inhibits iodoapamin binding. Both effects are due to a cation-induced modulation of the affinity of monoidoapamin for its receptor without any change of the maximal toxin binding capacity of synaptosomes. Guanidinium and molecules containing a guanidinium group are better inhibitors of iodoapamin binding than other inorganic cations or positively charged organic molecules.

Animals↗
PubMed1982

The Ca2+-dependent slow K+ conductance in cultured rat muscle cells: characterization with apamin.

The interaction of apamin, a bee venom neurotoxin, with rat skeletal muscle cell membranes has been followed using both an electrophysiological and a biochemical approach. Voltage-clamp analyses have shown that apamin, at low concentrations, specifically blocks the Ca2+-dependent slow K+ conductance in rat myotubes and myosacs . A specific binding site for apamin in rat muscle cell membranes has been characterized with the use of a highly radiolabelled apamin derivative [( 125I]apamin). The dissociation constant for the apamin-receptor complex is 36-60 pM and the maximal binding capacity is 3.5 fmol/mg of protein. [125I]Apamin binding to rat muscle membranes is displaced by quinine and quinidine with K0.5 values of 110 microM and 200 microM, respectively.

Action Potentials↗
PubMed1982

Apamin as a selective blocker of the calcium-dependent potassium channel in neuroblastoma cells: voltage-clamp and biochemical characterization of the toxin receptor.

This paper describes the interaction of apamin, a bee venom neurotoxin, with the mouse neuroblastoma cell membrane. Voltage-clamp analyses have shown that apamin at low concentrations specifically blocks the Ca2+-dependent K+ channel in differentiated neuroblastoma cells. Binding experiments with highly radiolabeled toxin indicate that the dissociation constant of the apamin-receptor complex in differentiated neuroblastoma cells is 15-22 pM and the maximal binding capacity is 12 fmol/mg of protein. The receptor is destroyed by proteases, suggesting that it is a protein. The binding capacity of neuroblastoma cells for radiolabeled apamin dramatically increases during the transition from the nondifferentiated to the differentiated state. The number of Ca2+-dependent K+ channels appears to be at most 1/5th the number of fast Na+ channels in differentiated neuroblastoma. The binding of radiolabeled apamin to its receptor is antagonized by monovalent and divalent cations. Na+ inhibition of the binding of 125I-labeled apamin is of the competitive type (Kd(Na+) = 44 mM). Guanidinium and guanidinated compounds such as amiloride or neurotensin prevent binding of 125I-labeled apamin, the best antagonist being neurotensin.

Animals↗
PubMed1981

Thymic involution in pregnant mice. I. Characterization of the remaining thymocyte subpopulations.

Pregnancy-induced thymic atrophy was studied in mice during the course of syngeneic gestation and the post-partum period. Cortical thymocytes were greatly reduced in number as shown by the binding of fluorescein-labelled PNA. The pool of steroid-resistant (SR) medullary thymocytes appeared unchanged in pregnant mice when studied by means of a specific heteroantiserum (SRCA). Therefore, in pregnant mice, these two surface markers demonstrated that thymic atrophy was linked to steroid-sensitive (SS) cortical cell reduction. The presumed hydrocortisone resistance of the mother's remaining thymocytes is not related to a difference in the number of steroid receptors as determined by 3H-dexamethasone binding.

Animals↗
PubMed1980

Steroid-induced inhibition of nucleoside uptake in isolated mouse thymocytes.

In view of the evidence suggesting a possible effect of high concentrations of steroids on membrane properties, we have investigated the effect of several steroid molecules on the uptake and incorporation of [3H]uridine is isolated mouse thymocytes. Our results demonstrate that the sex steroids, the estrogenic compound, diethylstilbestrol, and several non-hormonal steroid molecules induce a marked inhibition of nucleoside uptake. This effect, which occurs only at concentrations above 10(-6) M, is almost instantaneous but transient and does not therefore appear to be mediated through specific receptor occupancy. Since sex steroids have been shown to inhibit mitogen-induced blast transformation at concentrations close to 10(-5) M, we suggest that this membrane effect of sex steroids may partly explain their immunosuppressive effects.

Animals↗
PubMed1980

Effect of dexamethasone on cyclo-oxygenase activity in reno-medullary cells in culture.

The steroid-induced inhibition of prostaglandin secretion has been shown to be mediated through the interaction of the steroid with specific receptors and to require RNA and protein synthesis. At present the nature of the protein(s) involved is unknown although several suggestions have been made for the role of phospholipase A2. It has also been postulated that the early action of steroid is a stimulation of cyclo-oxygenase activity leading only secondarily to an inhibition of arachidonate supply. In this paper, we have therefore investigated the effect of dexamethasone on cyclo-oxygenase activity in cultures of rat reno-medullary interstitial cells. Pretreatment of the cells with the anti-inflammatory steroid dexamethasone induces a moderate increase in cyclo-oxygenase activity but this elevation does not appear sufficient to account for the inhibitory action of dexamethasone on PG secretion.

Animals↗