The gastrointestinal tract relies on robust mucosal defense mechanisms to protect against luminal insults, particularly acid in the upper intestine and pathogens in the lower gut. This study investigates the role of the electroneutral Na⁺-HCO₃⁻ cotransporter NBCn1 in maintaining acid-base homeostasis in the duodenum and supporting mucus layer formation in the colon. Using NBCn1 knockout (KO) mice, we employed in vivo two-photon confocal microscopy to monitor intracellular pH (pHi) in duodenal villous enterocytes during exposure to low-pH luminal solutions. In wild-type (WT) mice, pHi rapidly recovered following acid challenge, indicating efficient basolateral HCO₃⁻ import. However, in NBCn1 KO mice, this recovery was severely impaired, demonstrating that NBCn1 is essential for rapid pHi restoration after acidification.
Further analysis revealed that NBCn1-deficient duodenocytes failed to mount a protective HCO₃⁻ secretory response upon contact with acidic luminal contents. This was confirmed by single-pass perfusion and pH-stat titration, which showed a markedly reduced HCO₃⁻ secretion rate in KO mice compared to WT controls. These findings highlight NBCn1 as a key regulator of duodenal acid-base balance, enabling enterocytes to neutralize protons accumulated during luminal acid exposure and sustain a defensive bicarbonate-rich environment.
In the colon, NBCn1 was localized to the basolateral membrane of crypt cells, particularly goblet cells, which are responsible for mucus production. Despite minimal involvement in epithelial pHi regulation under experimental conditions, NBCn1 deficiency led to a significant delay in mucus layer build-up. In vivo imaging using fluorescent beads revealed that the adherent mucus layer formed more slowly and was thinner in KO mice. Immunohistochemical analysis confirmed a reduction in mucus layer thickness, often showing irregular structure and discontinuities. These results suggest that basolateral HCO₃⁻ uptake via NBCn1 is critical for optimal mucus release and expansion, likely by supporting intracellular HCO₃⁻ accumulation necessary for granule swelling and exocytosis.Antioxidant 245 In Vivo
Notably, surface pH alkalinization remained unaffected in NBCn1 KO colon, indicating that apical HCO₃⁻ secretion was not the primary defect.Menoxymycin B Anti-infection Instead, the impairment appears to lie in the cellular machinery driving mucus dynamics, underscoring NBCn1’s role beyond simple ion transport—it supports mucus barrier integrity through metabolic support of goblet cell function.PMID:34878700
Collectively, these findings demonstrate that NBCn1 plays distinct yet vital roles in intestinal mucosal protection: it enables rapid recovery from acid-induced intracellular acidification in the duodenum and facilitates efficient mucus layer formation in the colon. The differential functional impact highlights the segment-specific importance of NBCn1 in maintaining gastrointestinal homeostasis. Given its strong expression in human duodenum and colonic goblet cells, defective NBCn1 activity may contribute to pathologies such as peptic ulcers, inflammatory bowel disease, and cystic fibrosis-related intestinal dysfunction. Targeting NBCn1 could therefore offer novel therapeutic strategies for enhancing mucosal defense in gastrointestinal disorders.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com