Mechanisms of bicarbonate secretion in the equine colon ex vivo

Abstract

Abstract OBJECTIVE To examine bicarbonate (HCO3−) secretion ex vivo in the equine large colon to determine any differences between the right dorsal colon (RDC) and right ventral colon (RVC). The effect of phenylbutazone (PBZ) on HCO3− secretion was examined in the RDC. ANIMALS 14 healthy horses. PROCEDURES In anesthetized horses (n = 10), segments of mucosa from RDC and RVC were harvested to measure HCO3− secretion ex vivo with the pH Stat method. The effect of PBZ on HCO3− secretion in the RDC was studied in 4 additional horses. RESULTS Three distinct mechanisms of HCO3− secretion previously described in a murine model were confirmed in the equine colon. The RDC had a greater capacity for electrogenic, Cl−-independent HCO3− secretion than the RVC (P = 0.04). In the RDC, all HCO3− secretion was decreased by PBZ (P < 0.02) but was not studied in the RVC because of low baseline secretion. CLINICAL RELEVANCE Secretion of HCO3− by the RDC could play a pivotal role in equine colon physiology, because intense microbial fermentation in this site could require HCO3− secretion to buffer short-chain fatty acids. Inhibition of this secretion by PBZ could interfere with mucosal buffering and predispose to changes associated with right dorsal colitis.