Fiber-optic ammonia sensor for measuring synaptic glutamate and extracellular ammonia

Kar, Satyajit; Arnold, Mark A.

doi:10.1021/ac00044a024

Cited by 39 publications

(16 citation statements)

References 6 publications

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“…The ammonia sensor was made of a micropipette whose tip was filled with a droplet of fluorescent pH indicator covered with a gas-permeable membrane. This sensor is a miniaturized version of the sensor described by Kar and Arnold (1992). The method for fabricating this sensor was similar to that described by Elamari et al (1997), with some modifications.…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, we determined whether activation of glycolysis affected mitochondrial NADH. We tested the effect of NH 4 ϩ , first because biochemical evidence shows that NH 4 ϩ at 1 mM is an allosteric activator of phosphofructokinase (PFK), which is one of the enzymes controlling the glycolytic flux (Lowry and Passonneau, 1966), and second because stimulation of the isolated amphibian retina has been found to cause an increase in the concentration of ammonia released in the extracellular fluid (Kar and Arnold, 1992). In addition, deamination of glutamate by mitochondrial GDH would produce NH 4 ϩ .…”

Section: Glutamate Transport and Signalingmentioning

confidence: 99%

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Mechanisms of Glutamate Metabolic Signaling in Retinal Glial (Müller) Cells

et al. 2000

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Retinal Müller (glial) cells metabolize glucose to lactate, which is preferentially taken up by photoreceptor neurons as fuel for their oxidative metabolism. We explored whether lactate supply to neurons is a glial function controlled by neuronal signals. For this, we used subcellular fluorescence imaging and either amperometric or optical biosensors to monitor metabolic responses simultaneously from mitochondrial and cytosolic compartments of individual Müller cells from salamander retina. Our results demonstrate that lactate production and release is controlled by the combined action of glutamate and NH(4)(+), both at micromolar concentrations. Transport of glutamate by a high-affinity carrier can produce in Müller cells a rapid rise of glutamate concentration. In our isolated Müller cells, glutamine synthetase (GS) converted transported glutamate to glutamine that was released. This reaction, predominant when enough NH(4)(+) is available, was limited at micromolar concentrations of NH(4)(+), and more glutamate entered then as substrate into the mitochondrial tricarboxylic acid cycle (TCA). Increased production of glutamine by GS leads to increased utilization of ATP, some of which is generated glycolytically. Methionine sulfoximine, a specific inhibitor of GS, suppressed the stimulatory effect of glutamate and NH(4)(+) on glycolysis and induced massive entry of glutamate into the TCA cycle. The rate of glutamine production also determined the amount of pyruvate transaminated by glutamate to alanine. Lactate, alanine, and glutamine can be taken up and metabolized by photoreceptor neurons. We conclude that a major function of Müller glial cells is to nourish retinal neurons and to metabolize the neurotoxic ammonia and glutamate.

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Section: Methodsmentioning

confidence: 99%

Section: Glutamate Transport and Signalingmentioning

confidence: 99%

Mechanisms of Glutamate Metabolic Signaling in Retinal Glial (Müller) Cells

et al. 2000

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“…Using the above approach, biosensors for urea 96,97 and glutamate 53 have been fabricated by immobilising urease and glutamine oxidase, respectively, at the tip of the optical fibre ammonia sensor. In a different set-up, the measurement was made in a FIA manifold consisting of a urease membrane, and an integrated gas diffusion/detection unit.…”

Section: Nh 3 Transducersmentioning

confidence: 99%

“…However, the response times may also correspondingly increase due to the greater time required to establish the steady state conditions. 53 Response signals tend to level off though at much higher dye concentrations as a result of self-absorption of fluorescence by the indicator itself. Increased volumes of the internal solution are observed to result in larger signals up to a point where the pathlength no longer increases as the reservoir depth is increased.…”

Section: Nh 3 Transducersmentioning

confidence: 99%

Optical fibre biosensors based on immobilised enzymes

Kuswandi¹,

Andres²,

Narayanaswamy³

2001

Analyst

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“…Various schemes for measuring glutamate based on enzymatic assay have been developed [59][60][61][62][63][64][65][66][67]. With the utilization of glutamate dehydrogenase, coupled with cosubstrate NAD + , the product of the reaction, NADH, can be monitored either by fluorescence or by absorption.…”

confidence: 99%

Selective detection of neurotransmitters by fluorescence and chemiluminescence imaging

Wang

Yeung

2001

Pure and Applied Chemistry

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In recent years, luminescence imaging has been widely employed in neurochemical analysis. It has a number of advantages for the study of neuronal and other biological cells: (1) a particular molecular species or cellular constituent can be selectively visualized in the presence of a large excess of other species in a heterogeneous environment; (2) low concentration detection limits can be achieved because of the inherent sensitivity associated with fluorescence and chemiluminescence; (3) low excitation intensities can be used so that long-term observation can be realized while the viability of the specimen is preserved; and (4) excellent spatial resolution can be obtained with the light microscope so subcellular compartments can be identified. With good sensitivity, temporal and spatial resolution, the flux of ions and molecules and the distribution and dynamics of intracellular species can be measured in real time with specific luminescence probes, substrates, or with native fluorescence. A noninvasive detection scheme based on glutamate dehydrogenase (GDH) enzymatic assay combined with microscopy was developed to measure the glutamate release in cultured cells from the central nervous system (CNS). The enzyme reaction is very specific and sensitive. The detection limit with CCD imaging is down to µM levels of glutamate with reasonable response time. We also found that chemiluminescence associated with the ATP-dependent reaction between luciferase and luciferin can be used to image ATP at levels down to 10 nM in the millisecond time scale. Similar imaging experiments should be feasible in a broad spectrum of biological systems.

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Fiber-optic ammonia sensor for measuring synaptic glutamate and extracellular ammonia

Cited by 39 publications

References 6 publications

Mechanisms of Glutamate Metabolic Signaling in Retinal Glial (Müller) Cells

Mechanisms of Glutamate Metabolic Signaling in Retinal Glial (Müller) Cells

Optical fibre biosensors based on immobilised enzymes

Selective detection of neurotransmitters by fluorescence and chemiluminescence imaging

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