Age-related Regulation of Active Amino Acid Transport in the Ileum of Broiler Chickens

Broiler chickens grow rapidly within a short period; in this regard, our group had previously reported a decrease in the active transport of glucose in the intestines of broiler chickens with their growth. Therefore, in this study, we compared the active transport process of amino acids in the intestines between 1- and 5-week-old broilers using everted sac, Ussing chamber techniques, and real-time quantitative polymerase chain reaction (RT-PCR). The everted sac experiment showed that amino acids were absorbed from all segments of the small intestine in both age groups. There were no significant differences in the serosal to mucosal ratio between 1- and 5-week-old broilers. The Ussing chamber experiment showed that amino acid-induced short-circuit current (ΔIsc) in the ileal epithelium was significantly greater in the 5-week-old chickens than in the 1-week-old chicks (P=0.035). Membrane conductance, an indicator of ion permeability, showed no significant difference between the two groups. Moreover, the mRNA expression levels of amino acid transporters (ASCT1, EAAT3, B⁰AT1, and y⁺LAT1) were significantly elevated in the distal ileum of the 5-week-old broilers compared to those in the 1-week-old broilers (P<0.05), while no significant differences were observed in the mRNA levels of ATB0'⁺, B^0/+AT, rBAT, CAT1, and CAT2 in both groups. Our study provides clear evidence that age-dependent increase in the active transport of amino acid across the ileal epithelium is caused by the high expression of Na⁺-dependent amino acid transporters in broiler chickens.