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C Giaume

Publications and source records attributed to C Giaume.

At least 55 records · Page 3Linked to original sources
PubMed1996

[Communicating junctions of glial cells in the central nervous system].

In the brain, in vivo as in vitro, glial cells represent the main cell population which communicates through intercellular channels forming gap junctions. These cells, and specially the astrocytes, also express a large variety of ionic channels and membrane receptors. The combination of biochemical, immunological and electrophysiological techniques has allowed to determine that connexin 32 is present in oligodendrocytes while connexin 43 is the major junctional protein in astrocytes. The conductance and permeability of gap junctions in astrocytes are controlled by endogenous compounds released from neurons or endothelial cells. This suggests that gap junctional communication in astrocyte networks exhibits some degree of plasticity and are under the control of other brain cell populations. The expression of connexins and the regulation of junctional permeability in astrocytes may contribute to several glial functions such as intercellular calcium signalling and metabolic trafficking within the brain.

Animals↗
PubMed1995

Inhibition by anandamide of gap junctions and intercellular calcium signalling in striatal astrocytes.

Anandamide, an endogenous arachidonic acid derivative that is released from neurons and activates cannabinoid receptors, may act as a transcellular cannabimimetic messenger in the central nervous system. The biological actions of anandamide and the identity of its target cells are, however, still poorly documented. Here we show that anandamide is a potent inhibitor of gap-junction conductance and dye permeability in striatal astrocytes. This inhibitory effect is specific for anandamide as compared to co-released congeners or structural analogues, is sensitive to pertussis toxin and to protein-alkylating agents, and is neither mimicked by cannabinoid-receptor agonists nor prevented by a cannabinoid-receptor antagonist. Glutamate released from neurons evokes calcium waves in astrocytes that propagate via gap junctions, and may, in turn, activate neurons distant from their initiation sites in astrocytes. We find that anandamide blocks the propagation of astrocyte calcium waves generated by either mechanical stimulation or local glutamate application. Thus, by regulating gap-junction permeability, anandamide may control intercellular communication in astrocytes and therefore neuron-glial interactions.

Animals↗
PubMed1995

Homotypic and heterotypic coupling mediated by gap junctions during glial cell differentiation in vitro.

Intercellular communication mediated by gap junctions was investigated during oligodendrocyte differentiation in primary and secondary cell cultures from newborn and adult rats. Two types of communication were considered: ionic coupling and dye-coupling between similar oligodendrocytes selected at the same stage of differentiation (homotypic) and dye-coupling between oligodendrocytes and astrocytes (heterotypic). Intercellular diffusion of fluorescent probes and double whole-cell recordings were used to test the incidence of dye and ionic communication respectively. Progenitor cells, identified with A2B5 antibodies, were characterized by the absence of ionic and dye-coupling, whereas oligodendrocytes, identified with galactosylceramide antibodies, exhibited both types of communication. This homotypic coupling was inhibited by various uncoupling agents, but unaffected by treatments which increased the intracellular concentration of cAMP. In cocultures of astrocytes and oligodendrocytes, Lucifer yellow and sulphorhodamine B were exchanged in both directions. This heterotypic dye-coupling, which could be blocked by octanol, first appeared after 3 weeks in culture and increased to an incidence of 25% after 6 weeks, a developmental pattern comparable to homotypic dye-coupling between oligodendrocytes. In contrast, during the same period, progenitors and microglia were never observed to be dye-coupled with astrocytes.

Animals↗
PubMed1995

Gap junctions in brain glial cells and development.

In mammalian brain, glia are likely the most abundant and widespread cell population connected by gap junctions. Here, we summarize recent findings concerning the distribution, expression, and regulation of gap junction proteins in different glial subtypes and their possible roles in modulating the function of the nervous system. Intercellular communication through gap junctions is proposed to be one of the required interactions between cells during development, and we discuss how gap junctions could participate in development of brain glial cells.

Aging↗
PubMed1994

Glial receptors and their intervention in astrocyto-astrocytic and astrocyto-neuronal interactions.

As shown on cultured astrocytes from the mouse, in the presence of adenosine deaminase, 2-chloroadenosine by acting on A1-adenosine receptors potentiated the activation of phospholipase C induced by the alpha 1-adrenergic agonist, methoxamine. This potentiation required the presence of external calcium and was blocked by pertussis toxin. Moreover, this potentiation resulted from a cascade of events: activation (by calcium and protein kinase C) of a phospholipase A2 coupled to A1-adenosine receptors, release of arachidonic acid, which inhibited the reuptake of glutamate into astrocytes and finally additional activation of phospholipase C by externally accumulated glutamate through metabotropic receptors. The effects of 2-chloroadenosine and methoxamine were respectively mimicked by somatostatin and substance P while endothelins reproduced the combined effects of 2-chloroadenosine and methoxamine. Conditioned media from treated astrocytes enriched in glutamate stimulated phospholipase C in cultured striatal neurones. In addition, glutamate alone was also found to stimulate phospholipase A2 in astrocytes through receptors exhibiting a pharmacological profile distinct from metabotropic receptors coupled to phospholipase C and the glutamate response was potentiated by ATP. Moreover, the neuronal arachidonic acid production evoked by glutamate was potentiated by acetylcholine. Finally, the combined application of 2-chloroadenosine and methoxamine on striatal astrocytes reduced the permeability of gap junctions between astrocytes and this response was mimicked by arachidonic acid. Together, these results emphasized the contribution of astrocytes in the regulation of glutamatergic transmission.

2-Chloroadenosine↗
PubMed1994

The first developing "mixed" synapses between vestibular sensory neurons mediate glutamate chemical transmission.

In the present study, the nature of the synaptic transmission responsible for a monophasic potential generated by vestibular nerve stimulation of the principal cells in the chick tangential nucleus was established. This work was performed in slice preparations at the critical embryonic age of 15-16 days, the time of first observation of morphologically mixed (chemical and electrical) synapses at the axosomatic endings called spoon endings. The spoon endings are formed by the primary vestibular fibers with the largest diameters, the colossal vestibular fibers. This monophasic potential fits the criteria for chemical rather than electrical transmission due to the following responses in most cases: (i) the absence of collision between a direct spike initiated by depolarization in the principal cell and a vestibular-evoked action potential; (ii) failure to follow high frequency stimulation (up to 50 Hz); (iii) sensitivity to low calcium solution (0.1 mM). These tests indicate that strong electrical coupling between spoon endings and principal cells does not prevail at this stage. The recordings were obtained from principal cells injected intracellularly with biocytin, allowing their identification by morphological criteria. The lack of tracer coupling between the stained principal cells and their innervating vestibular fibers (n = 17) is consistent with the absence of electrical coupling. Identification of the neurotransmitter involved in this vestibular response was achieved by bath application of glutamate receptor antagonists, DL-2-amino-5-phosphonovaleric acid (40 microM) and 6-cyano-7-nitro-quinoxaline-2,3-dione (10 microM), which blocked transmission reversibly. These results suggest that at the onset of formation of these "mixed" vestibular synapses, the gap junctions identified morphologically are likely not functional, and that the main response of the principal cells to vestibular nerve stimulation is mediated by glutamate.

2-Amino-5-phosphonovalerate↗
PubMed1994

Is intercellular communication via gap junctions required for myoblast fusion?

Fusion of myoblasts to form syncitial muscle cells results from a complex series of sequential events including cell alignment, cell adhesion and cell communication. The aim of the present investigation was to assess whether intercellular communication through gap junctions would be required for subsequent membrane fusion. The presence of the gap junction protein connexin 43 at areas of contact between prefusing rat L6 myoblasts was established by immunofluorescent staining. These myoblasts were dye-coupled, as demonstrated by the use of the scrape-loading/dye transfer technique. L6 myoblast dye coupling was reversibly blocked by heptanol in short term experiments as well as after chronic treatment. After a single addition of 3.5 mM heptanol, gap junctions remained blocked for up to 8 hours, then this inhibitory effect decreased gradually, likely because the alcohol was evaporated. Changing heptanol solutions every 8 hours during the time course of L6 differentiation resulted in a lasting drastic inhibition of myoblast fusion. We further investigated the effect of heptanol and of other uncoupling agents on the differentiation of primary cultures of embryonic chicken myoblasts. These cells are transiently coupled by gap junctions before myoblast fusion and prolonged application of heptanol, octanol and 18-beta-glycyrrhetinic acid also inhibited their fusion. The effect of heptanol and octanol was neither due to a cytotoxic effect nor to a modification of cell proliferation. Moreover, heptanol treatment did not alter myoblast alignment and adhesion. Taken together these observations suggest that intercellular communication might be a necessary step for myoblast fusion.

Alcohols↗
PubMed1993

Effects of general anesthetics on intercellular communications mediated by gap junctions between astrocytes in primary culture.

BACKGROUND: Astrocytes represent a major nonneuronal cell population in the central nervous system (CNS) and are actively involved in several brain functions. These cells are coupled by gap junctions (GJ) into a syncytial-like network resulting in cellular communication through ionic and metabolic exchange between adjacent astrocytes. Whether anesthetics affect astrocyte function is not known. In the present study, the effects of general anesthetics on GJ permeability were investigated in primary cultures of mouse striatal astrocytes. METHODS: Junctional permeability was determined by using the fluorescent probe Lucifer yellow and the scrape loading/dye transfer technique. Confluent cells were preincubated 5 min with various concentrations of anesthetic agents and GJ permeability was estimated by measuring the area occupied by the dye from digitalized images taken 8 min after cell loading. RESULTS: Of the intravenous anesthetics tested, only propofol (P: 10(-4) M, P < 0.01 and 10(-5) M, P < 0.05) and etomidate (ET: 10(-4) M, P < 0.05, but not 10(-5) M) induced a significant reduction of GJ permeability. In contrast, diazepam (10(-5) M), morphine (10(-4) M), ketamine (10(-4) M), thiopental (10(-4) M), and clonidine (10(-7) M) did not affect junctional permeability. In addition, the halogenated anesthetics halothane, enflurane, and isoflurane induced a dose-dependent closure of GJ. For halothane, enflurane, and isoflurane, the maximum effect was achieved with a 10(-4) M, 1.6 x 10(-3) M, and 10(-3) M anesthetic concentration, respectively. Removal of volatile anesthetics resulted in the restoration of the control fluorescence area between 15 and 45 min. The time course of recovery of GJ permeability was examined more precisely for shorter periods of halothane administration (5 min, 1 mM). Under these conditions, the rate of dye spread returned to control values following anesthetic washout, while, during the same period of time, complete uncoupling of GJ was still observed in the presence of a 1 mM halothane concentration. CONCLUSIONS: These results indicate that general anesthetics differentially affect GJ permeability in cultured astrocytes. This uncoupling effect (closure of gap junctions) may contribute to the mechanisms of action of some anesthetic agents (primarily volatile anesthetics) at the level of the CNS by altering astrocyte communication.

Anesthetics↗
PubMed1991

Adrenergic regulation of intercellular communications between cultured striatal astrocytes from the mouse.

The permeability of gap junctions in cultured striatal astrocytes was investigated by the scrape-loading/dyetransfer technique. Prolonged application of norepinephrine (NE) (10 microM) reduced by half the extent of dye (Lucifer yellow) spread. This effect was linked to the activation of alpha 1-adrenergic receptors since it was mimicked by methoxamine and antagonized by prazosin. The adenosine agonist 2-chloroadenosine (10 microM), which potentiates the NE-evoked activation of phospholipase C (PLC) in striatal astrocytes, also potentiated the NE-evoked closure of gap junctions, the effect being as important as that observed with the uncoupling agent octanol. Measurements of inositol phospholipid turnover performed in identical experimental conditions revealed a close relationship between the extent of PLC activation and the magnitude of the uncoupling process. The effect of NE was mimicked by both phorbol ester and arachidonic acid, suggesting that biochemical events linked to PLC stimulation such as protein kinase C activation and/or eicosanoid production are likely involved in the NE-induced uncoupling. In addition, in the presence of a cAMP phosphodiesterase inhibitor, the stimulation of beta-adrenergic receptors by isoproterenol (10 microM) led to a large increase in cAMP accumulation correlated with an extension of dye diffusion. This observation suggests that junctional permeability could also be controlled by a cAMP-dependent mechanism. Altogether these results indicate that intercellular communication between cultured astrocytes can be regulated by different second messenger pathways as a result of the action of neurotransmitters on their receptors.

Animals↗
PubMed1991

Gap junctions in cultured astrocytes: single-channel currents and characterization of channel-forming protein.

Currents from gap junction channels were recorded from pairs of astrocytes in primary culture using the double whole-cell recording technique. In weakly coupled pairs, single-channel events could be resolved without pharmacological uncoupling treatment. Under these conditions, unitary conductance was 56 +/- 7 pS, and except for multiples of this value, no other level of conductance was observed consistently. To characterize the type of junctional protein constituting astrocyte gap junction channels, immunological and biochemical experiments were carried out on the same material. Specific cDNA probes for three connexins identified in mammals (Cx26, Cx32, and Cx43) showed that only Cx43 mRNA was expressed in cultured astrocytes. The presence of Cx43 protein in cultured astrocytes was demonstrated by immunoblotting, immunofluorescence, and immunogold labeling using anti-peptide antibodies specific to Cx43. These results strongly suggest that gap junctions in astrocytes have a 50-60 pS unitary conductance associated with channels composed of Cx43 protein.

Animals↗
PubMed1989

Electrophysiological study of the tangential vestibular nucleus of the chick embryo "in vitro".

The two main neuron types of the tangential vestibular nucleus, the principal and the elongate cells, were investigated using intracellular recordings on brain slice preparations of 15-16 day chick embryos. Their identification was confirmed by intracellular injections of the fluorescent dye, Lucifer yellow. The passive membrane properties of these two neuron types were not sufficient criteria for their identification, whereas their responses to current pulse injections were distinctive. The elongate cells showed a nonlinear current-voltage relationship to hyperpolarizing currents and they fired repetitively at high frequencies without accommodation when the cells were depolarized. Neither of these two properties were observed in principal cells. Synaptic responses to vestibular nerve stimulation were different for the two neurons. The elongate cells responded gradually to increasing stimulus intensity, while the principal cells exhibited two clear postsynaptic responses: a low-threshold action potential initiated by an all-or-none EPSP, and a second, higher threshold, longer latency and graded EPSP. The latter EPSP is characterized by a slow rise time and a long duration. The findings obtained at this embryonic age are consistent with data concerning principal and elongate cell innervation by different caliber fibers comprising the vestibular nerve. The early EPSP recorded from the principal cells is attributed to the colossal fibers, which are vestibular afferents of large diameter forming calyciform contacts, the spoon endings, exclusively on the principal cells. The other synaptic responses recorded from the elongate and principal cells are due to the firing of different classes of small vestibular afferents. These experiments were performed in this new preparation at a critical age for the development of the spoon endings.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1989

Arachidonic acid closes gap junction channels in rat lacrimal glands.

The effects of arachidonic acid (AA) on gap junction conductance of rat lacrimal glands have been studied with the double patch-clamp technique. Extracellular application of 50-100 microM AA for a few minutes induced a closure of gap junction channels. This effect was mimicked by linoleic acid and by other non-degradable fatty acids (myristic and lauric), and was not blocked by inhibitors of AA metabolism. This suggests that the active molecule was the fatty acid itself, and not one of its oxidative derivatives. Inhibitors of AA metabolism caused a certain degree of uncoupling by themselves, probably due to the accumulation of AA. This effect was reduced in the presence of 10 microM 4-bromophenacylbromide, an inhibitor of phospholipase A2. The effect of AA did not seem to be mediated by an increase of intracellular Ca concentration, nor by a change in the activity of guanylate or adenylate cyclases, nor by activation of protein kinase C. Therefore it could be attributed to a direct effect of AA on gap junctions. Analysis of single gap junction channel currents showed that AA-induced closure of these channels resulted from a change in the number of open channels, and not from a reduction of their conductance. Finally, acetylcholine-induced closure of gap junction channels was not primarily mediated by an increase in AA concentration, although such an increase may well follow the activation of muscarinic receptors and play a role in the acetylcholine effect.

Acetophenones↗
PubMed1988

Acetylcholine-induced closure of gap junction channels in rat lacrimal glands is probably mediated by protein kinase C.

In rat lacrimal gland cells, application of acetylcholine (ACh) opens Ca-dependent channels and closes gap junction channels. We have shown previously that the increase in intracellular calcium concentration induced by ACh, is not required for the closure of gap junctions. We have examined the effects of activators of protein kinase C on gap junction conductance measured with the double patch-clamp technique. This conductance was markedly reduced by incubating the cell pairs for a few minutes with 100 nM phorbol dibutyrate (PdBu). Two membrane permeant analogues of diacylglycerol, OAG (1-oleoyl-2-acetyl-glycerol) and DOG (1,2-dioleoyl-glycerol) also induced a closure of gap junction channels. This effect was observed in the concentration range 10-100 microM when the diacylglycerol was added on intact cells, and at 75 microM when it was applied on dialysed cells. The cell uncoupling was not mediated by phosphatidate, a degradation product of OAG, nor by a phospholipase A2-induced increase in arachidonate concentration. The OAG-induced closure of gap junction channels reversed spontaneously upon prolonged exposure (more than 90 min at 37 degrees C) to 25 microM OAG. After a prolonged OAG treatment, the ability of ACh to uncouple the cells was markedly reduced. ACh induced uncoupling was modulated to some extent by intracellular Ca and had an absolute requirement for Mg. These results indicate that ACh-induced closure of gap junction channels may be mediated by PKC.

Acetylcholine↗
PubMed1987

Voltage-clamp analysis of a crayfish rectifying synapse.

1. The rectifying crayfish giant motor synapse has been studied in the second abdominal ganglion, using the double-voltage-clamp technique which allowed direct measurements of junctional current at various fixed transjunctional potentials. 2. The transjunctional potential (Vj), defined as the difference between the voltages recorded in the lateral giant axon and the giant motor fibre, was varied from -70 to +50 mV, the minimum and maximum junctional chord conductances (gmin and gmax, respectively) were found to be 1.2 +/- 1.3 microS (n = 10) and 22.9 +/- 6.3 microS (n = 10), respectively. 3. For a given Vj, changes in the lateral giant axon or giant motor fibre membrane potential over a range of +/- 30 mV around their resting levels did not influence the junctional permeability (gj), indicating that the inside-outside potential of the junctional channel does not control gj. 4. Therefore, the steady-state junctional chord conductances were dependent only upon Vj. 5. The voltage dependence of the chord conductance was well fitted by a modified Boltzmann relation given by the equation (Formula: see text) with the constants: A = 0.15 +/- 0.03 mV-1 (n = 10) and V0 = 28 +/- 4 mV (n = 10); the latter two parameters were also found to be independent of both transmembrane potentials. 6. The junctional currents were already constant 1 ms after step changes in the junctional voltage; this was three orders of magnitude faster than the other known examples of voltage-controlled gap junctions between embryonic cells. 7. Our results may be interpreted by a highly voltage-dependent probability of opening of the junctional channels. They also suggest that the gap-junction channels forming the giant motor synapse respond very rapidly to potential and that the hemi-channels which constitute them may not be symmetric.

Action Potentials↗
PubMed1986

Evidence for ionic coupling between MDCK cells at non-confluent and confluent stages of culture.

The possibility of current flow between epithelial cells (MDCK) has been evaluated using intracellular electrophysiological techniques. We report here that a significant electrotonic coupling was found in this material at all ages of culture. This observation contrasts with previous reports that confluent MDCK are not ionically coupled and lack gap junctions. Alternative mechanisms for such coupling are considered, with emphasis on the role of tight junctions, should the absence of gap junctions be confirmed.

Animals↗
PubMed1984

Voltage-dependent dye coupling at a rectifying electrotonic synapse of the crayfish.

At the crayfish giant motor synapse, the lateral giant axon (l.g.a.) and the giant motor fibre (g.m.f.) form an electrotonic junction which exhibits two states of ionic coupling (Furshpan & Potter, 1959a; Giaume & Korn, 1983). Junctional conductance is low at resting membrane potentials (i.e. with lateral axon more negative than the motor fibre) and high when the polarity of the voltage difference (delta V) across the synapse is reversed. For these two states of conductance, junctional permeability was investigated using the intercellular tracer Lucifer Yellow. The dye was ionophoretically injected into either the presynaptic (l.g.a.) or the post-synaptic (g.m.f.) cell. In the high conductance state (delta V greater than 0), fluorescence was detected in both neurones whether Lucifer Yellow had been injected pre- or post-synaptically. By contrast, at the resting junctional polarization (delta V less than 0) Lucifer Yellow spread from the giant axon to the g.m.f., but not from the g.m.f. to the giant axons. These data demonstrate that dye transfer at the giant motor synapse, like ionic coupling, is sensitive to junctional polarization and is more marked in the high conductance state. Possible explanations for the asymmetry observed in the low conductance state are discussed.

Animals↗
PubMed1983

Application of antimony microelectrodes to intracellular pH monitoring.

Some novel studies of the properties of the antimony microelectrode used for intracellular pH measurements are described. First, it is shown that currents in the picoampere range, such as those encountered as leakage in some electrometers, induce important changes in pH sensitivity. The response time of the electrode has also been measured and indicates that the electrode exhibits a rapid time course which would be very useful for dynamic cytoplasmic pH investigations. An example of internal pH recording during cellular acidification in Xenopus laevis oocyte is also presented.

Animals↗