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Jean-Yves Chatton

Publications and source records attributed to Jean-Yves Chatton.

8 recordsLinked to original sources
PubMed2006

In situ fluorescence imaging of glutamate-evoked mitochondrial Na+ responses in astrocytes.

Astrocytes can experience large intracellular Na+ changes following the activation of the Na+-coupled glutamate transport. The present study investigated whether cytosolic Na+ changes are transmitted to mitochondria, which could therefore influence their function and contribute to the overall intracellular Na+ regulation. Mitochondrial Na+ (Na+(mit)) changes were monitored using the Na+-sensitive fluorescent probe CoroNa Red (CR) in intact primary cortical astrocytes, as opposed to the classical isolated mitochondria preparation. The mitochondrial localization and Na+ sensitivity of the dye were first verified and indicated that it can be safely used as a selective Na+(mit) indicator. We found by simultaneously monitoring cytosolic and mitochondrial Na+ using sodium-binding benzofuran isophthalate and CR, respectively, that glutamate-evoked cytosolic Na+ elevations are transmitted to mitochondria. The resting Na+(mit) concentration was estimated at 19.0 +/- 0.8 mM, reaching 30.1 +/- 1.2 mM during 200 microM glutamate application. Blockers of conductances potentially mediating Na+ entry (calcium uniporter, monovalent cation conductances, K+(ATP) channels) were not able to prevent the Na+(mit) response to glutamate. However, Ca2+ and its exchange with Na+ appear to play an important role in mediating mitochondrial Na+ entry as chelating intracellular Ca2+ with BAPTA or inhibiting Na+/Ca2+ exchanger with CGP-37157 diminished the Na+(mit) response. Moreover, intracellular Ca2+ increase achieved by photoactivation of caged Ca2+ also induced a Na+(mit) elevation. Inhibition of mitochondrial Na/H antiporter using ethylisopropyl-amiloride caused a steady increase in Na+(mit) without increasing cytosolic Na+, indicating that Na+ extrusion from mitochondria is mediated by these exchangers. Thus, mitochondria in intact astrocytes are equipped to efficiently sense cellular Na+ signals and to dynamically regulate their Na+ content.

Amino Acid Transport System X-AG↗
PubMed2005

Flash photolysis using a light emitting diode: an efficient, compact, and affordable solution.

Flash photolysis has become an essential technique for dynamic investigations of living cells and tissues. This approach offers several advantages for instantly changing the concentration of bioactive compounds outside and inside living cells with high spatial resolution. Light sources for photolysis need to deliver pulses of high intensity light in the near UV range (300-380 nm), to photoactivate a sufficient amount of molecules in a short time. UV lasers are often required as the light source, making flash photolysis a costly approach. Here we describe the use of a high power 365 nm light emitting diode (UV LED) coupled to an optical fiber to precisely deliver the light to the sample. The ability of the UV LED light source to photoactivate several caged compounds (CMNB-fluorescein, MNI-glutamate, NP-EGTA, DMNPE-ATP) as well as to evoke the associated cellular Ca(2+) responses is demonstrated in both neurons and astrocytes. This report shows that UV LEDs are an efficient light source for flash photolysis and represent an alternative to UV lasers for many applications. A compact, powerful, and low-cost system is described in detail.

Animals↗
PubMed2004

Astrocytes generate Na+-mediated metabolic waves.

Glutamate-evoked Na+ increase in astrocytes has been identified as a signal coupling synaptic activity to glucose consumption. Astrocytes participate in multicellular signaling by transmitting intercellular Ca2+ waves. Here we show that intercellular Na+ waves are also evoked by activation of single cultured cortical mouse astrocytes in parallel with Ca2+ waves; however, there are spatial and temporal differences. Indeed, maneuvers that inhibit Ca2+ waves also inhibit Na+ waves; however, inhibition of the Na+/glutamate cotransporters or enzymatic degradation of extracellular glutamate selectively inhibit the Na+ wave. Thus, glutamate released by a Ca2+ wave-dependent mechanism is taken up by the Na+/glutamate cotransporters, resulting in a regenerative propagation of cytosolic Na+ increases. The Na+ wave gives rise to a spatially correlated increase in glucose uptake, which is prevented by glutamate transporter inhibition. Therefore, astrocytes appear to function as a network for concerted neurometabolic coupling through the generation of intercellular Na+ and metabolic waves.

4-Chloro-7-nitrobenzofurazan↗
PubMed2004

Involvement of inositol 1,4,5-trisphosphate in nicotinic calcium responses in dystrophic myotubes assessed by near-plasma membrane calcium measurement.

In skeletal muscle cells, plasma membrane depolarization causes a rapid calcium release from the sarcoplasmic reticulum through ryanodine receptors triggering contraction. In Duchenne muscular dystrophy (DMD), a lethal disease that is caused by the lack of the cytoskeletal protein dystrophin, the cytosolic calcium concentration is known to be increased, and this increase may lead to cell necrosis. Here, we used myotubes derived from control and mdx mice, the murine model of DMD, to study the calcium responses induced by nicotinic acetylcholine receptor stimulation. The photoprotein aequorin was expressed in the cytosol or targeted to the plasma membrane as a fusion protein with the synaptosome-associated protein SNAP-25, thus allowing calcium measurements in a restricted area localized just below the plasma membrane. The carbachol-induced calcium responses were 4.5 times bigger in dystrophic myotubes than in control myotubes. Moreover, in dystrophic myotubes the carbachol-mediated calcium responses measured in the subsarcolemmal area were at least 10 times bigger than in the bulk cytosol. The initial calcium responses were due to calcium influx into the cells followed by a fast refilling/release phase from the sarcoplasmic reticulum. In addition and unexpectedly, the inositol 1,4,5-trisphosphate receptor pathway was involved in these calcium signals only in the dystrophic myotubes. This surprising involvement of this calcium release channel in the excitation-contraction coupling could open new ways for understanding exercise-induced calcium increases and downstream muscle degeneration in mdx mice and, therefore, in DMD.

Aequorin↗
PubMed2003

GABA uptake into astrocytes is not associated with significant metabolic cost: implications for brain imaging of inhibitory transmission.

Synaptically released glutamate has been identified as a signal coupling excitatory neuronal activity to increased glucose utilization. The proposed mechanism of this coupling involves glutamate uptake into astrocytes resulting in increased intracellular Na+ (Nai+) and activation of the Na+/K+-ATPase. Increased metabolic demand linked to disruption of Nai+ homeostasis activates glucose uptake and glycolysis in astrocytes. Here, we have examined whether a similar neurometabolic coupling could operate for the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), also taken up by Na+-dependent transporters into astrocytes. Thus, we have compared the Nai+ response to GABA and glutamate in mouse astrocytes by microspectrofluorimetry. The Nai+ response to GABA consisted of a rapid rise of 4-6 mM followed by a plateau that did not, however, significantly activate the pump. Indeed, the GABA transporter-evoked Na+ influxes are transient in nature, almost totally shutting off within approximately 30 sec of GABA application. The metabolic consequences of the GABA-induced Nai+ response were evaluated by monitoring cellular ATP changes indirectly in single cells and measuring 2-deoxyglucose uptake in astrocyte populations. Both approaches showed that, whereas glutamate induced a robust metabolic response in astrocytes (decreased ATP levels and glucose uptake stimulation), GABA did not cause any measurable metabolic response, consistent with the Nai+ measurements. Results indicate that GABA does not couple inhibitory neuronal activity with glucose utilization, as does glutamate for excitatory neurotransmission, and suggest that GABA-mediated synaptic transmission does not contribute directly to brain imaging signals based on deoxyglucose.

Animals↗
PubMed2003

Brain-derived neurotrophic factor stimulates energy metabolism in developing cortical neurons.

Brain-derived neurotrophic factor (BDNF) promotes the biochemical and morphological differentiation of selective populations of neurons during development. In this study we examined the energy requirements associated with the effects of BDNF on neuronal differentiation. Because glucose is the preferred energy substrate in the brain, the effect of BDNF on glucose utilization was investigated in developing cortical neurons via biochemical and imaging studies. Results revealed that BDNF increases glucose utilization and the expression of the neuronal glucose transporter GLUT3. Stimulation of glucose utilization by BDNF was shown to result from the activation of Na+/K+-ATPase via an increase in Na+ influx that is mediated, at least in part, by the stimulation of Na+-dependent amino acid transport. The increased Na+-dependent amino acid uptake by BDNF is followed by an enhancement of overall protein synthesis associated with the differentiation of cortical neurons. Together, these data demonstrate the ability of BDNF to stimulate glucose utilization in response to an enhanced energy demand resulting from increases in amino acid uptake and protein synthesis associated with the promotion of neuronal differentiation by BDNF.

Amino Acids↗
PubMed2003

Glial glutamate transporters mediate a functional metabolic crosstalk between neurons and astrocytes in the mouse developing cortex.

Neuron-glia interactions are essential for synaptic function, and glial glutamate (re)uptake plays a key role at glutamatergic synapses. In knockout mice, for either glial glutamate transporters, GLAST or GLT-1, a classical metabolic response to synaptic activation (i.e., enhancement of glucose utilization) is decreased at an early functional stage in the somatosensory barrel cortex following activation of whiskers. Investigation in vitro demonstrates that glial glutamate transport represents a critical step for triggering enhanced glucose utilization, but also lactate release from astrocytes through a mechanism involving changes in intracellular Na(+) concentration. These data suggest that a metabolic crosstalk takes place between neurons and astrocytes in the developing cortex, which would be regulated by synaptic activity and mediated by glial glutamate transporters.

Amino Acid Transport System X-AG↗