Cellular uptake of valine by lactating porcine mammary tissue.

Abstract

The cellular uptake of branched-chain amino acids in mammary tissue is important for understanding their role in milk synthesis in the sow. This study characterized the kinetic properties and substrate specificity of the valine uptake system in the porcine mammary gland. Mammary tissue was collected from lactating sows at slaughter and tissue explants were incubated in media containing isosmotic salt and amino acids of interest, plus [3H]valine tracer. Valine uptake was time-dependent and was dependent on the presence of sodium, as indicated by a reduction in uptake when sodium in the medium was replaced by choline. The valine transport system in porcine mammary tissue had a Km of 0.64 mM, a Vmax of 1.84 mmol-kg cell water(-1) 30 min(-l), and a Kd (diffusion constant) of 1.16 L x kg cell water(-1) x 30 min(-1). Valine uptake was inhibited by leucine and alpha-aminoisobutyric acid and by high concentrations of L-alanine, L-lysine, cycloleucine, L-glutamine, and L-methionine, but not by 2-(methyl-amino)-isobutyric acid. This transport system is the primary system responsible for uptake of valine, and probably other branched-chain amino acids, in lactating sow mammary tissue. Physiological concentrations of valine in the blood are below the Km of the specific valine transport system and well below the diffusion uptake capabilities. The kinetic parameters of this valine transport system should not be limiting to valine uptake for milk protein synthesis. However, competition of valine uptake with branched-chain amino acids, as well as with other amino acids, may affect valine uptake in lactating tissue.

Phenylalanine and valine differentially stimulate milk protein synthetic and energy-mediated pathway in immortalized bovine mammary epithelial cells

“…Positive effects of branched-chain amino acids (BCAAs) on both milk and body protein synthesis have previously been documented [17]. In porcine mammary tissue, after the addition of VAL to the culture medium, the amount of intracellular VAL exceeded the amount of extracellular VAL within 15-30 min [18]. In this experiment, only cellular protein concentrations were significantly increased after VAL treatment (Fig.…”

Dietary protein concentration affects plasma arteriovenous difference of amino acids across the porcine mammary gland1

“…Uptake inhibition among AA has been shown to occur in a number of tissues, including mammary tissue, and thus may explain the curvilinear relationship between CP intake and AA a-v observed in this study, as well as that observed by Guinard and Rulquin (1994). In this study, in contrast to the cationic and small neutral AA, arterial concentrations of the large neutral AA, in particular the BCAA leucine and isoleucine, largely increased in sows fed the Excess CP diet, which may have contributed to the quadratic response, albeit a trend, between CP intake and valine a-v. For instance, uptake of valine by the lactating sow mammary tissue has been shown to be strongly inhibited by physiological concentration of leucine (Jackson et al, 2000). A similar explanation for the quadratic response in lysine a-v may be proposed, based on the findings that high concentrations of neutral AA both inhibit lysine influx into and stimulate lysine efflux from rodent mammary tissue (Shennan et al, 1994;Calvert and Shennan, 1996).…”

Combination of histidine, lysine, methionine, and leucine promotes β-casein synthesis via the mechanistic target of rapamycin signaling pathway in bovine mammary epithelial cells

“…Some studies have shown that high Leu is known to negative interaction transport of Ile and Val and enhance catabolism of Ile and Val. Leucine inhibits Val uptake in lactating porcine mammary tissue (Jackson et al, 2000) and in lactating dairy mammary tissue (Haque et al, 2013). Consequently, duodenal infusions of 40 g of Leu/d to corn-based diets improved both milk protein content and yield on diets limiting in Lys or Met (Rulquin and Pisulewski, 2006).…”