Microelectrode Sensing of Adenosine/Adenosine‐5′‐triphosphate with Fast‐Scan Cyclic Voltammetry

2010

ACS Chem. Neurosci.

Adenosine is an important neuromodulator in the brain. Traditionally, adenosine is thought to arise in the extracellular space by either an extracellular mechanism, where it is formed outside the cell by the breakdown of released ATP, or an intracellular mechanism, where adenosine made inside the cell is transported out. Recently, a proposed third mechanism of activity dependent adenosine release has also been proposed. Here, we used fast-scan cyclic voltammetry to compare the time course and mechanism of adenosine formation evoked by either low- or high-frequency stimulations in striatal rat brain slices. Low-frequency stimulations (5 pulses at 10 Hz) resulted in an average adenosine efflux of 0.22 ± 0.02 μM, while high-frequency stimulations (5 pulses, 60 Hz) evoked 0.36 ± 0.04 μM. Blocking intracellular formation by inhibiting adenosine transporters with S-(4-nitrobenzyl)-6-thioinosine (NBTI) or propentofylline did not decrease release for either frequency, indicating that the release was not due to the intracellular mechanism. Blocking extracellular formation with ARL-67156 reduced low-frequency release about 60%, but did not affect high-frequency release. Both low- and high-frequency stimulated release were almost completely blocked by removal of calcium, indicating activity dependence. Reducing dopamine efflux did not affect adenosine release but inhibiting ionotropic glutamate receptors did, indicating that adenosine release is dependent on downstream effects of glutamate. Therefore, adenosine release after short, high-frequency physiological stimulations is independent of transporter activity or ATP metabolism, and may be due to direct release of adenosine after glutamate receptor activation.

Section: Resultsmentioning

confidence: 98%

Adenosine Release Evoked by Short Electrical Stimulations in Striatal Brain Slices Is Primarily Activity Dependent

Pajski

2010

ACS Chem. Neurosci.

“…ATP has the same oxidation reaction as adenosine, and the traces are similar except that carbon-fiber microelectrodes are more sensitive to adenosine. 16 , 18 , 19 Dopamine has a peak at 0.6 V and is shown as a control for comparison purposes. 34 − 36 …”

Section: Resultsmentioning

confidence: 99%

“… 16 Adenosine poses a specific challenge due to its relatively high E 0 (∼1.30 V), 17 so a switching potential of 1.45–1.50 V is necessary with FSCV. 16 , 18 , 19 Adenosine is a neuromodulatory molecule found in the brain 20 − 22 and is neuroprotective during conditions of ischemia 23 , 24 and hypoxia. 25 , 26 Detection of adenosine using FSCV 3 , 16 , 18 is beneficial for understanding how adenosine functions on the subsecond to second time scale.…”

mentioning

confidence: 99%

Sawhorse Waveform Voltammetry for Selective Detection of Adenosine, ATP, and Hydrogen Peroxide

Ross

2014

Anal. Chem.

Fast-scan cyclic voltammetry (FSCV) is an electrochemistry technique which allows subsecond detection of neurotransmitters in vivo. Adenosine detection using FSCV has become increasingly popular but can be difficult because of interfering agents which oxidize at or near the same potential as adenosine. Triangle shaped waveforms are traditionally used for FSCV, but modified waveforms have been introduced to maximize analyte sensitivity and provide stability at high scan rates. Here, a modified sawhorse waveform was used to maximize the time for adenosine oxidation and to manipulate the shapes of cyclic voltammograms (CVs) of analytes which oxidize at the switching potential. The optimized waveform consists of scanning at 400 V/s from −0.4 to 1.35 V and holding briefly for 1.0 ms followed by a ramp back down to −0.4 V. This waveform allows the use of a lower switching potential for adenosine detection. Hydrogen peroxide and ATP also oxidize at the switching potential and can interfere with adenosine measurements in vivo; however, their CVs were altered with the sawhorse waveform and they could be distinguished from adenosine. Principal component analysis (PCA) was used to determine that the sawhorse waveform was better than the triangle waveform at discriminating between adenosine, hydrogen peroxide, and ATP. In slices, mechanically evoked adenosine was identified with PCA and changes in the ratio of ATP to adenosine were observed after manipulation of ATP metabolism by POM-1. The sawhorse waveform is useful for adenosine, hydrogen peroxide, and ATP discrimination and will facilitate more confident measurements of these analytes in vivo.

“…The lower sensitivity for ATP is likely due to poor adsorption because of the negative charge or steric hindrance of the phosphate groups that prevent the adenine moiety from being properly aligned for oxidation. 38 …”

Section: Resultsmentioning

confidence: 99%

Nafion–CNT coated carbon-fiber microelectrodes for enhanced detection of adenosine

Ross

2012

Analyst

109

Adenosine is a neuromodulator that regulates neurotransmission. Adenosine can be monitored using fast-scan cyclic voltammetry at carbon-fiber microelectrodes and ATP is a possible interferent in vivo because the electroactive moiety, adenine, is the same for both molecules. In this study, we investigated carbon-fiber microelectrodes coated with Nafion and carbon nanotubes (CNTs) to enhance the sensitivity of adenosine and decrease interference by ATP. Electrodes coated in 0.05 mg/mL CNTs in Nafion had a 4.2 ± 0.2 fold increase in current for adenosine, twice as large as for Nafion alone. Nafion-CNT electrodes were 6 times more sensitive to adenosine than ATP. The Nafion-CNT coating did not slow the temporal response of the electrode. Comparing different purine bases shows that the presence of an amine group enhances sensitivity and that purines with carbonyl groups, such as guanine and hypoxanthine, do not have as great an enhancement after Nafion-CNT coating. The ribose group provides additional sensitivity enhancement for adenosine over adenine. The Nafion-CNT modified electrodes exhibited significantly more current for adenosine than ATP in brain slices. Therefore, Nafion-CNT modified electrodes are useful for sensitive, selective detection of adenosine in biological samples.