Abstract
Sulforhodamine 101 (SR101) is widely used as a marker of astrocytes. In this study we investigated labeling of astrocytes by SR101 in acute slices from the ventrolateral medulla and the hippocampus of transgenic mice expressing EGFP under the control of the astrocyte-specific human GFAP promoter. While SR101 efficiently and specifically labeled EGFP-expressing astrocytes in hippocampus, we found that the same staining procedure failed to label astrocytes efficiently in the ventrolateral medulla. Although carbenoxolone is able to decrease the SR101-labeling of astrocytes in the hippocampus, it is unlikely that SR101 is taken up via gap-junction hemichannels because mefloquine, a blocker for pannexin and connexin hemichannels, was unable to prevent SR101-labeling of hippocampal astrocytes. However, SR101-labeling of the hippocampal astrocytes was significantly reduced by substrates of organic anion transport polypeptides, including estron-3-sulfate and dehydroepiandrosterone sulfate, suggesting that SR101 is actively transported into hippocampal astrocytes.
Highlights
Astrocytes are important players in neuronal networks
The synthetic glycyrrhetinic acid derivative carbenoxolone has been shown to block Sulforhodamine 101 (SR101)-labeling of astrocytes [7], it is not yet clear if this is due to its action on gapjunctions and hemichannels or a yet unknown, maybe indirect mechanism
It was obvious that labeling of ventrolateral medulla (VLM)-astrocytes with SR101 was not sufficient for the reliable identification of astrocytes (Figure 1B)
Summary
Astrocytes are important players in neuronal networks. They maintain the extracellular milieu by removal of potassium and neurotransmitters like glutamate and modulate synaptic transmission by releasing gliotransmitters [1,2,3]. Sulforhodamine 101 (SR101) has been used for specific visualization of astrocytes in cortex and hippocampus [6,7,8,9]. During hypoxia SR101 can enter hippocampal neurons via hemichannels [12]. It is not known how the specific loading of SR101 into astrocytes is achieved under normoxic conditions. SR101 is widely used as a marker for astrocytes in different brain regions [13,14,15] even despite the fact that sulforhodamine 101 has been found to trigger epileptic activity in the hippocampus [16]
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