Mechanism Underlying Astrocytic Uptake of Sulforhodamine 101 (SR101)
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Date
2025-03
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Abstract
Sulforhodamine 101 (SR101) is a commonly used chemical marker for astrocytes and is particularly useful in functional in vivo and in situ studies. However, the mechanism underlying the astrocytic uptake of SR101 remains elusive. Serendipitously, we found that SR101 uptake can be fully inhibited by meclofenamic acid (MFA). The MFA-mediated SR101 uptake inhibition is characterized by a non-competitive binding of MFA to the SR101 uptake pathway, a rapid inhibitory time course (T50, 0.4925 min), and high efficacy (IC50, 4.428 µM). Therefore, MFA emerges as a useful inhibitor to further explore the mechanism of SR101 uptake in astrocytes. In a transcriptome study, the slco1c1 mRNAs, a gene encoding L-thyroxine (T4) transporter (OATP1C1), showed high astrocyte expression. To explore slco1c1 as a potential SR101 uptake pathway, we pre-incubated acute hippocampal slices with 10 µM T4 for 20 min. This resulted in a 95% inhibition of SR101 uptake. Inhibition of OATP1C1 should lead to a buildup of ambient T4. To examine if T4 could affect neuronal excitability, we examine the electrophysiological responses of CA1 pyramidal neurons to 10 µM T4. Elevated ambient T4 appeared to attenuate the excitability of CA1 pyramidal neurons. Thus, our study has identified MFA as a potent SR101 uptake inhibitor in astrocytes. Additionally, we show that L-thyroxine competitively inhibits SR101 uptake in astrocytes, implying that slco1c1 is likely the transporter that mediates the SR101 uptake in astrocytes. Potentially, inhibition of OATP1C1 has an inhibitory impact on the excitability of CA1 pyramidal neurons.
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Health Under the Microscope (The Ohio State University Denman Undergraduate Research
Forum)
Keywords
Astrocytes, Sulforhodamine 101 (SR101)