Short-chain fatty acid transport and its effects on ion transport by rabbit cecum

Short-chain fatty acid (SCFA) metabolism and transport were examined in vitro across isolated rabbit cecal epithelia whose primary function is absorption of these solutes. This study shows that although there was some low-level metabolism of SCFAs to ketone bodies by the isolated cecum, a significantly higher oxygen consumption was sustained for a longer time period by tissues incubated in glucose-containing salines. The cecum supported a significant net secretory flux of acetate (J net Ac- = -1.13 +/- 0.13 mu eq X cm-2 X h-1) and propionate (J net Pr- = -0.61 +/- 0.14 mu eq X cm-2 X h-1). This study also shows that glucose significantly enhanced short-circuit current (Isc), tissue conductance (Gt), and sodium transport across this tissue. Neither Ac- nor Pr- enhanced net sodium flux (J net Ac-) but Pr- significantly reduced net chloride flux (J net Cl-), whereas Ac- had no effect. The increase in Isc and Gt observed in the presence of SCFAs was attributable to the presence of SCFA in the serosal bathing solution alone. To explain the latter finding and the unexpected finding of SCFA secretion, the existence of an electrogenic anion (HCO3-) secretory pathway is postulated. It is suggested that this system can accommodate SCFAs in vitro and that it is a Na+-dependent system located on the basolateral membrane of the cecal cell.