A balanced supply of dietary proteins and amino acids (AAs) is necessary for the optimal growth, development, and reproduction of animals. AA uptake requires numerous transport systems that vary in their substrate specificity, affinity, and velocity. AA transporters not only synchronize the transport of AAs into cells but also act as transceptors?That can sense AAs and activate signaling pathways.

As pig strains may vary in their capacity to recognize changes in AA concentration in body fluids, the utilization of free AAs may also differ among pig strains. According to Ph.D candidate LIU Yingying from Institute of Subtropical Agriculture, Chinese Academy of Science(ISA), differences among different strains of pigs in their muscle growth, meat quality, and intermuscular adipose deposition, may lead to dietary protein-dependent differences in AA metabolism.

In their recent research, LIU and her colleagues analyzed the effect of dietary protein intake on mRNA levels for key transporters and receptors of AAs and peptides in skeletal muscle. A total of 96 barrows (48 purebred Bama mini-pigs representing the fatty genotype, and 48 Landrace pigs representing the lean genotype) were randomly assigned to either a low- or adequate-protein treatment diet. The experimental period commenced at 5 weeks of age and extended to the finishing period, which divided into nursery, growing, and finishing phases.

The results showed that the concentrations of free AAs in the plasma and muscle decreased as the age of the pigs increased. In addition, a strain ?growth phase interaction was observed for the free AA pool in the plasma and muscle. The low-protein diet upregulated the mRNA levels for taste receptor type 1 member 1/ member 3 involved in glutamate binding, but downregulated the mRNA levels for proton-assisted AA transporters and ASC-like Na+-dependent neutral AA transporter, which transport neutral AAs into muscles. Bama mini-pigs had higher mRNA levels for L-type AA transporter 1, sodium-coupled neutral AA transporter 2, and excitatory AA carrier 1, but a lower mRNA level for H+/peptide co-transporter 1, compared with Landrace pigs.

In summary, the genetic background and dietary level of protein intake markedly affected free AA concentrations in pig plasma and skeletal muscle, as well as mRNA levels for key AA receptors and transporters in skeletal muscle. These effects of genotype and diet varied with the developmental stage of the animals. Collectively, our findings indicate that adequate provision of dietary protein plays an important role in regulating profiles of free AA pools and expression of key AA/peptide transporters/transceptors in a genotype- and tissue-specific manner.

The article has been published on Amino Acids (DOI 10.1007/s00726-015-2066-2), Details can be found at http://www.ncbi.nlm.nih.gov/pubmed/26255284

Contact: YIN Yulong