Monocarboxylate 4 mediated butyrate transport in a rat intestinal epithelial cell line

Abstract

Background: Short chain fatty acids (SCFA) are absorbed by carrier mediated uptake in the small intestine by pH-dependent SCFA/HCO3 (-) exchangers on the apical membrane of epithelial cells. Conventional assumption is that MCT1 mediates SCFA/HCO3 (-) exchange in the intestine. Further, due to the presence of multiple such anion exchangers, the identity of the intestinal SCFA/HCO3 (-) has been controversial.

Aims: The aim of this study was to determine the identities of the butyrate transporter in the intestinal epithelial cells (IEC-18).

Methods: IEC-18 cells were treated with specific siRNAs for MCT1 and MCT4, and butyrate and lactate uptake studies were performed.

Results: Alpha-cyano-4-hydroxycinnamic acid inhibited lactate uptake but not butyrate uptake in IEC-18 cells, indicating that these two substrates are transported via two different transporter systems. MCT1 siRNA treatment abolished both MCT1 mRNA by more than 95 % and protein expression by 83 % as evidenced by RTQ-PCR and western blotting experiments. However, MCT1 siRNA treatment inhibited butyrate uptake upto 24 %, whereas it inhibited lactate uptake significantly by 70 %. Treatment with MCT4 siRNA inhibited MCT4 mRNA expression by 75 % and protein expression by 85 % in these cells. MCT4 siRNA inhibited butyrate uptake by 40 %. Further, several non-steroidal anti-inflammatory drugs (NSAIDs) are transported by the butyrate transporter. Finally, MCT4 siRNA inhibited salicylate uptake by 27 % indicating direct evidence for the transport of salicylate by MCT4.

Conclusions: These data indicate that MCT1 is the high affinity lactate transporter and MCT4 is the high affinity butyrate transporter in the intestinal epithelial cell line IEC-18.