Expression of Na–H exchanger-8 isoform is suppressed in experimental colitis in adult rat: lack of reversibility by dexamethasone

Abstract

Objectives. Mechanism of the apical transporter Na–H exchanger-8 (NHE-8) regulation was investigated by examining the effects of anti-inflammatory dexamethasone in experimental colitis. In addition, its localization was investigated in the lipid rich membrane domain called membrane rafts. Material and methods. Colitis was induced by trinitrobenzene sulfonic acid (TNBS) and colon segments were removed from 5 day post-TNBS and used to estimate the levels of NHE-8 protein and mRNA using ECL western blot analysis and a competitive RT-PCR method. Myeloperoxidase activity, malondialdehyde levels and histologic changes were evaluated. Results. NHE-8 protein level was decreased in inflamed colon and was not reversed by dexamethasone. However, mRNA levels remained unchanged in inflamed colon. The levels of NHE-8 protein and mRNA were not significantly different in non-colitic control as compared to dexamethasone treated non-colitis. Elevation of myeloperoxidase activity, malondialdehyde and infiltration of inflammatory cells in inflamed colon were suppressed by dexamethasone treatment of colitis significantly. Furthermore, NHE-8 protein was not detected in the detergent resistant membrane (DRM) or lipid rafts, but was present in the detergent sensitive membrane (DRS) fractions. Actin showed its partition similar to NHE-8. On the contrary, NHE-3 was present in both DRM and DRS fractions. Flotillin-1 and caveolin were enriched in the fractions designated as lipid rafts. Conclusions. These findings demonstrate the suppression of NHE-8 protein in inflamed adult rat colon, which seems to be regulated post-transcriptionlly. Furthermore, the absence of NHE-8 in lipid rafts suggests its regulation independent of cAMP or recycling through endocytosis unlike NHE-3 isoform.

Key Words::

• Caveolin
• colitis
• flotillin
• inflammation
• membrane rafts
• MDA
• MPO
• NHE-8

Acknowledgments

The Kuwait University Research Administration for financial support through a student research grant MY04/09, College of Graduate Studies, the Research Core Facility, Faculty of Medicine, Kuwait University, Kuwait and Prof Khalid Khan for his assistance in histology.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.