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B Dufy

Publications and source records attributed to B Dufy.

At least 73 records · Page 4Linked to original sources
PubMed1987

Signal transduction mechanisms in cultured CNS neurons and clonal pituitary cells.

The experimental accessibility of monolayer culture has been used to study signal transduction mechanisms in primary CNS neurons and clonal pituitary cells. Here we review results on two signals representative of the emerging diversity of mechanisms discovered in all species studied thus far. One is mediated by micromolar concentrations of the amino acid GABA at postsynaptic membranes throughout the mammalian CNS and involves transient activation of Cl- ion channels whose distribution of conducting periods accounts for the millisecond time course of the signal. This signal serves to depress the probability that the target cell will trigger an action potential. The signal intensifies as the postsynaptic membrane is depolarized and can be modulated by clinically important drugs, primarily through changes in channel kinetics. The other signal involves nanomolar concentrations of the peptide TRH, which stimulates secretion of prolactin from clonal "GH3" pituitary cells. Intracellular recordings of GH3B6 cells show that TRH triggers a complex electrical response lasting several minutes. The response consists of Ca2+-activated K+ conductance followed by Ca2+-action potential activity. Whole-cell patch recordings, which rapidly dialyze the cell, can eliminate the TRH-induced changes in membrane excitability. Inclusion of aqueous lysates of the GH3B6 clone or the soluble second messenger factors inositol trisphosphate (IP3) or protein kinase (PKC) can restore various aspects of the change in membrane excitability. Thus, TRH alters ion conductance mechanisms through a second messenger cascade likely to involve IP3-mediated mobilization of Ca2+ from the endoplasmic reticulum and transient translocation of PKC from cytoplasm to plasma membrane. These synaptic and extrasynaptic signals reflect some of the diversity of transduction mechanisms involved in intercellular communication.

Amino Acids↗
PubMed1987

Bradykinin parallels thyrotropin-releasing hormone actions on prolactin release from rat anterior pituitary cells.

Bradykinin (BK), a nonapeptide, originally discovered in blood, is also present in neurons and fibers of the hypothalamus. We tested the putative releasing factor properties of BK on prolactin (PRL) release from anterior pituitary cells in vitro. BK stimulated the release of PRL in a dose-dependent manner, the threshold concentration being in the range. 0.1-1.0 nM. The release of PRL induced by BK at 1 nM concentration was about 2-fold, delayed and sustained over many minutes. Higher concentrations of BK stimulated PRL release in two phases. The shape of the BK-induced PRL release was superficially similar to that induced by thyrotropin-releasing hormone (TRH). 10 nM BK and 10 nM TRH induced about a 4-fold increase in PRL release within 5 min, followed by a gradual recovery to basal secretion. These results indicate that this peptide can act directly at the anterior pituitary gland to release PRL. Phorbol ester also promoted PRL release over the range of 1-10 nM, but the time course of the release was somewhat different.

Animals↗
PubMed1987

Electrical properties of cultured human adrenocorticotropin-secreting adenoma cells: effects of high K+, corticotropin-releasing factor, and angiotensin II.

ACTH-secreting pituitary adenoma cells were cultured from specimens obtained by transphenoidal hypophysectomy in five patients with Cushing's disease. The majority of adenoma cells (90%) stained specifically with antiserum against human ACTH. The electrophysiological properties and response to hormones of these cells were studied with intracellular recording techniques under current clamp and voltage clamp conditions. Most (80%) of the cells fired action potentials that were Ca2+-dependent inasmuch as they were blocked by Co2+ (5 mM) and by removal of Ca2+ from the medium, but were unaffected by tetrodotoxin (0.3 mM) and by Na+ removal. The cells responded to factors known to stimulate ACTH release, including high K+, CRF, and angiotensin II (AII). High K+ (50 mM) induced a membrane depolarization in association with an increase in conductance. CRF (100 nM) produced a depolarization, a decrease in conductance, an increase in spike firing, and an increase in spike duration. Although AII was inactive in ordinary recordings, in cells loaded with lithium (Li+) to promote the phospholipid-dependent second messenger system, the peptide produced an increase in spike firing and spike duration with no change in membrane potential. The combination of CRF and AII (CRF + AII; 100 nM each) in Li+-loaded cells caused a greater excitatory effect than either peptide alone. Under voltage clamp, the response either to CRF or to CRF + AII could be attributed, at least in part, to the inhibition of a slow, voltage-dependent K+ current that is persistently active at resting potential. These results indicate that modulation of action potential firing may be an early step in the regulation of ACTH release from pituitary cells by known secretagogues. Since action potentials in these cells are associated with Ca2+ entry, the resulting changes in intracellular Ca2+ levels could mediate the effects of the hormones on secretion.

Action Potentials↗
PubMed1987

Intracellular Ca2+-dependent protein kinase C activation mimics delayed effects of thyrotropin-releasing hormone on clonal pituitary cell excitability.

Biochemical and spectrophotometric studies of second messenger pathways transducing TRH signals in clonal pituitary (GH) cells have shown that TRH induces rapid turnover of phosphoinositides and changes in cytoplasmic Ca2+ as well as activation of protein kinase C (PKC) and secretion of PRL. Here we have used classical microelectrode and contemporary patch pipette recording techniques under current-clamp conditions to compare the effects of TRH receptor-coupled stimulation with direct activation of PKC on the excitability of GH3/B6 cells. With high resistance microelectrodes TRH induced a complex sequence of changes in membrane properties consisting of an initial 20- to 30-mV hyperpolarization associated with an increase in membrane conductance lasting less than a minute, followed by several minutes of low amplitude fluctuations and action potential activity superimposed on a modest increase in input resistance. Active phorbol ester induced a slowly developing hyperpolarization of about 5 mV and a modest increase in input resistance, followed by several minutes of low amplitude fluctuations and spontaneous action potential activity. Both the peptide- and phorbol ester-evoked changes in excitability were attenuated or completely lost during patch recordings in the whole cell mode. Dilute aqueous lysates of the clone restored various phases of the electrical response. The low amplitude fluctuations and action potential activity phase could be induced by either TRH or phorbol ester if the cells were dialyzed with intracellular electrolyte containing PKC and at least 50 nM Ca2+. These results demonstrate that the phosphoinositide/PKC circuit activated by TRH in clonal pituitary cells has electrically detectable effects on cell excitability, and these help to explain TRH's actions on electrical activity.

Action Potentials↗
PubMed1987

[Ketoconazole inhibits the conductance K+ induced by thyreoliberin (TRH) in GH3 cells].

Ketoconazole an imidazole derivative used in clinical practice as an antifungal medicine interferes with the phospholipid dependent "second messenger" pathway. In this work we show that in the GH3 clonal cell line, ketoconazole (10 microM) inhibits part of the complex pattern of electrical activity induced by Thyrotropin-Releasing Hormone (TRH, 10 nM). The phase blocked by ketoconazole represents the Ca2+ -activated K+ conductance.

Cell Line↗
PubMed1986

Rundown of GH3 cell K+ conductance response to TRH following patch recording can be obviated with GH3 cell extract.

GH3/B6 pituitary cells release prolactin (PRL) in response to thyrotropin releasing hormone (TRH). Electrophysiological assays of individual GH3 cells with sharp high-resistance microelectrodes have revealed complex effects of TRH on membrane excitability consisting of a transient hyperpolarization (1), which is thought to result from activation of Ca-dependent K+ conductance (2), followed by a prolonged phase of spontaneous, Ca-dependent action potential activity (3). Using the whole-cell patch recording (WCR) technique (4), we have found that these TRH actions on GH3 excitability rapidly rundown following patch recording. When the supernatant from osmotically lysed GH3 cells was added to the WCR patch pipette, the K+ conductance response was not only promoted but well-maintained. The results indicate that diffusible factors mediate these TRH actions and further, that the WCR technique should be useful in identifying different second messengers and elucidating their roles in membrane excitability and PRL secretion.

Adenosine Triphosphate↗
PubMed1986

[Bradykinin stimulates prolactin release in vitro].

Bradykinin (BK) is a nonpeptide, originally discovered in blood; recently BK has been localized in neurons and fibers of the hypothalamus. BK is a vasoactive substance which is involved in pain, inflammation and oedema. The present study demonstrates that BK is also a potent stimulator of prolactin (PRL) release from anterior pituitary cells in vitro. A significant enhancement of the release of PRL is observed at 1 nM BK. The stimulation of PRL release by BK is dose-dependent. This work shows that anterior pituitary cells in culture may serve as a useful model system in which to study the mechanism of action of BK.

Animals↗
PubMed1984

[Influence of calcitonin and ACTH 4-10 on the phenomena of mammary tumor induction by a chemical carcinogen, 7,12-dimethylbenzanthracene].

We have studied the effects of a single intravenous injection of calcitonin (TCT) and ACTH 4-10 on the induction of mammary tumors by Dimethylbenz(a)anthracene (DMBA) in Sprague Dawley female rats. In the animals which received TCT, we observed a significant delay in the occurrence of tumors, and a decrease in their number and size. Administration of ACTH 4-10 gave similar results. The inhibitory effect of TCT on tumoral induction and growth can be explained by the hypocalcemic action of TCT. Conversely, ACTH 4-10 having no effect on calcemia, the mechanism of action of this peptide on tumoral induction remains to be elucidated.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1983

Hyperglycemic effect in the rabbit induced by ACTH4-10.

In the rabbit, a single i.v. administration of ACTH4-10 (130 micrograms/kg) induces hyperglycemia. As ACTH4-10 also induces hypocalcemia and inhibits insulin secretion, we suggest that hypocalcemia, inhibition of insulin secretion, and hyperglycemia, are closely related.

Adrenocorticotropic Hormone↗
PubMed1983

[Histamine and prolactin liberation in the rhesus monkey].

The effect of intra venous (i.v.) or intra cerebroventriculaire (i.c.v.) administration of histamine (HA) on plasma prolactin (PRL) levels was investigated in ovariectomized Rhesus Monkeys. Intra venous injection of 50 micrograms/kg HA increased the plasma PRL concentration but icv administration of 10 and 50 micrograms decreased PRL plasma levels. Intra venous injection of 2-thiazolyl-éthylamine, a H1 receptor agonist, rapidly stimulated PRL release (peak PRL concentration at 5 min) suggesting a direct effect on the pituitary. In contrast intra venous administration of the H2 receptor agonist, impromidine, inhibited PRL release at low doses. High doses of impromidine increased PRL concentrations but this effect was delayed (PRL peak values were reached at 20 minutes). Our results show that HA may influence PRL release in the primate via H1 and H2 receptors located at both pituitary and central levels.

Animals↗
PubMed1983

[Properties of membrane ionic currents in pituitary clone cells].

Membrane ionic currents of the GH3 pituitary cell line have been studied using voltage clamp techniques. The inward current is completely blocked by cobalt (Co2+) ions and appeared to be carried by calcium ions. Three outward currents can be differentiated on the ground of kinetics and pharmacological studies: a transient current blocked by 4-aminopyridine (4 AP) and two delayed outward current which are voltage dependent. One is blocked by tetraethylammonium (TEA); the second is blocked by Co2+ and represents a calcium-activated potassium conductance.

4-Aminopyridine↗
PubMed1982

Calcium-activated and voltage-dependent potassium conductances in clonal pituitary cells.

Voltage clamp recordings of GH3/B6 pituitary cells reveal the presence of non linear steady state membrane properties at the level of the resting potential (about -41 mV). Clamping the cells to potentials more depolarized than -60 mV is associated with a potential dependent increase in membrane conductance and membrane current variance. Tetra-ethylammonium (TEA), Cobalt (Co2+) and methoxy-verapamil (D-600) each attenuate these potential-dependent changes. Spectral analysis of membrane current fluctuations shows that power spectral densities calculated for fluctuations occuring over the -70 to -40 mV range decline monotonically as a function of frequency, while spectra derived from fluctuations obtained over the -20 mV to 0 mV range decline as the square of frequency and are usually well fitted by a single Lorentzian equation. The half-power frequency of these spectra varies from 45 to 65 Hz. If we assume that the activities of two-state (open-closed) ion channels underlie the electrical behaviour of the membrane at the resting potential and at more depolarized levels, then the results suggest the presence of K+ ion channels whose activation depends both on potential and Ca2+ ions. These K+ ion channels have estimated electrical properties (conductance : 15 ps ; duration : 3 msec) similar to those present in other excitable membranes.

Animals↗