Expression of system N protein mRNA, but not system A or L, is upregulated by ileal epithelia of growing beef cattle in response to increased luminal supply of energy but not amino acids

Abstract

To complete our in vivo study of how basal expression profiles of 20 amino acid (AA) transporter genes respond to increases in luminal supply of substrates or energy in the small intestine, total RNA was extracted from duodenal (D), jejunal (J), and ileal (I) epithelia of 18 ruminally and abomasally catheterized Angus steers (BW ? 260 kg) fed an alfalfa‐cube based diet at 1.3× NEm requirement and infused for 14 to 16 d with either (n = 6) water (basal) or corn starch hydrolysate (20% ME intake) into rumen (increased microbial AA) or abomasum (increased glucose/energy). The effect of infusion treatments on expression of mRNA encoding systems A (ATA1, 2, 3), N (SN1, 2), and L (LAT1, 2) neutral AA transporters was evaluated by real‐time RT‐PCR methodoloy. Basal expression of all mRNA but ATA3 differed (P = 0.06) among D, J, and I: ATA1, D=J>I; ATA2, D=J, D=I, J>I; SN1, D>J=I; SN2, J>D=I; LAT1, D=J>I; LAT2, D=J, J=I, D<I. Increased luminal AA or energy supply did not affect (P > 0.15) the mRNA content of these neutral AA transporters except that expression of SN1 and SN2 mRNA by I was increased (P = 0.08) 57 and 51%, respectively, with increased luminal energy supply. This latter finding suggests that luminal energy supply may limit I expression of SN1 and SN2 mRNA. This study was funded by a USDA‐ARS Special Cooperative Agreement Grant.