Clonidine enhances type-2 cationic amino acid transporter transcription in endotoxin-activated murine macrophages

Background: We sought to evaluate the effects of clonidine on type-2 cationic amino acid transporter (CAT-2) transcription in endotoxin-activated murine macrophages. Methods: To determine the effects of clonidine on CAT-2 transcription, confluent murine macrophages (RAW264.7 cells) were treated with 1x phosphate buffered saline, clonidine (1000μM), lipopolysaccharide (LPS, 100ng/mL), or LPS plus clonidine (10, 100, or 1000μM). After reacting with LPS for 18 hours or a comparable duration in groups without LPS, cell cultures were harvested and the CAT-2 mRNA concentration was assayed. To determine the stability of CAT-2 mRNA, confluent macrophages were treated with LPS or LPS plus clonidine (100μM). After reacting with LPS for 6 hours, CAT-2 transcription was terminated and the stability of CAT-2 mRNA was determined. Results: The CAT-2 mRNA concentration of cell cultures receiving LPS plus clonidine (100μM) or LPS plus clonidine (1000μM) were significantly higher than that of the cell cultures receiving LPS alone, whereas the CAT-2 mRNA concentrations of cell cultures receiving LPS plus clonidine (10μM) was comparable to that of cell cultures receiving LPS alone. The data indicated that clonidine significantly enhanced LPS-induced CAT-2 transcription. The estimated half-life of CAT-2 mRNA of cell cultures receiving LPS was similar to that of cell cultures receiving LPS plus clonidine. These results indicated that clonidine did not affect CAT-2 mRNA stability. Conclusion: Clonidine enhances CAT-2 transcription in endotoxin-activated murine macrophages.