Abstract
In this study, we investigated a mechanistic link between Na–H exchanger-1 (NHE-1) and carbonic anhydrase (CA) in experimental colitis induced in the rats by intrarectal administration of trinitrobenzenesulphonic acid (TNBS). Western blot analysis showed CA-I and CA-II as the major isoforms and CA-IV as a minor one in the colon, and they all are expressed as minor isoforms in the ileum. Co-immunoprecipitation and confocal immunofluorescence microscopy showed colocalization of NHE-1 with CA-I and CA-II, but not with CA-IV. TNBS significantly reduced the levels of NHE-1 and CA protein isoforms in the colon, but not in the uninflamed ileum. A similar reduction profile of the expression of CA isozymes was also obtained in ex vivo treatment of normal colon strips with TNF-α. The level of uncoupling as detected by co-immunoprecipitation was significantly more pronounced. A peptide (83 aa) from the NHE-1 C-terminus demonstrated binding of CA-II only, but not of the CA-I or CA-IV isoform. Furthermore, the profile of inflammatory test markers confirmed inflammation in the tissue used. These findings taken together suggest an inflammation-induced uncoupling of CA and NHE-1, which might be a putative mechanism for reducing the activity of NHE-1 in experimental colitis. This uncoupling might lead to an intracellular accumulation of H+, resulting in acidosis and necrosis in the inflamed colon.
Highlights
Carbonic anhydrase (CA), a Zn metalloenzyme, catalyzes a reversible conversion of CO2 to HCO3 −and H+ under normal physiological conditions, and participates in the regulation of intracellular pH, and electroneutral uptake of NaCl and water from the renal tubules and gastrointestinal (GI)tract [1,2]
The noncolitis control animals, on the contrary gained a significant body to their weight on day 0
inflammatory bowel diseases (IBDs) are associated with dysregulation of electrolyte and water homeostasis, which is attributed to an IBDs impairment of ion transport mechanisms
Summary
Carbonic anhydrase (CA), a Zn metalloenzyme, catalyzes a reversible conversion of CO2 to HCO3 −and H+ under normal physiological conditions, and participates in the regulation of intracellular pH, and electroneutral uptake of NaCl and water from the renal tubules and gastrointestinal (GI)tract [1,2]. The cytoplasmic isozymes, CA-I and CA-II, produce H+ and HCO3 − from CO2 , which are expelled out by NHE-1 and Cl− /HCO3 - transporters, respectively [8,9,10]. The CA-IV isozyme, present on the apical membrane in colonocytes, converts HCO3 −. To CO2 , which on percolation through the plasma membrane may fuel the cytoplasmic CA isozymes. A compromise, in the expression of these isozymes is likely to impair ion transport in inflammatory bowel diseases (IBDs). Crohn’s disease and ulcerative colitis represent IBDs, which are chronic inflammatory and debilitating conditions of the GI tract. IBD conditions are frequently associated with diarrhea, pain, and altered muscle contractility. With regard to the role of other transporters in relation to Na–H exchanger-1 (NHE-1), Biomolecules 2019, 9, 700; doi:10.3390/biom9110700 www.mdpi.com/journal/biomolecules
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