Characteristics of a cationic amino acid transport system in the basolateral membrane of the cat salivary epithelium

• Published in: The Journal of physiology 1984-06, Vol.351 (1), p.123-134
• Main Authors: Mann, G E, Wilson, S M, Yudilevich, D L
• Format: Article
• Language: English
• Subjects: Amino Acids - pharmacology; Animals; Basement Membrane - metabolism; Biological and medical sciences; Biological Transport; Cations; Cats; Female; Fundamental and applied biological sciences. Psychology; Kinetics; Lysine - antagonists & inhibitors; Lysine - metabolism; Male; Mouth. Exocrine and endocrine salivary glands. Teeth. Esophagus; Sodium - pharmacology; Stereoisomerism; Submandibular Gland - metabolism; Vertebrates: digestive system
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1984.sp015237

The specificity and kinetics of L-lysine influx across the basolateral surface of the cat salivary epithelium have been investigated in the perfused cat submandibular gland using a high-resolution, paired-tracer dilution technique. L-lysine influx was measured at several different perfusate concentrations (0.05-2.5 mM) and was found to be saturable. A Michaelis-Menten analysis based on a single entry site gave a Km of 0.49 +/- 0.08 mM and a Vmax of 231 +/- 20 nmol/min X g. The uptake of L-lysine was highly stereospecific and markedly inhibited by L-arginine (0.25-2.5 mM). The inhibitor constant (Ki) was 0.23 mM, suggesting that the carrier had a greater affinity for L-arginine than L-lysine. When the inhibitory effects of L-histidine (0.5-10 mM) were examined the Ki, estimated at 10 mM, was 4.6 mM. Nine other neutral amino acids (L-alanine, L-serine, L-cysteine, glycine, L-proline, L-homoserine, L-leucine, L-phenylalanine and L-glutamine), and an acidic amino acid (L-aspartate) were also tested at 10 mM and, although several caused inhibition, the Ki was always at least 20 times higher than the measured Km for L-lysine. It is concluded the carrier is highly specific for the L-form of the basic amino acids. The sodium dependence of L-lysine influx was investigated over a range of L-lysine concentrations (0.05-1 mM), and total removal of sodium from the perfusate had no effect on L-lysine influx. In the presence of sodium, L-homoserine, an amino acid not normally present in animal tissues, inhibited L-lysine influx (Ki = 13 mM). This inhibition was not observed in the absence of sodium, and contrasts with the observation that the inhibitory action of L-histidine was sodium independent. The present data suggest that a specific cationic amino acid transport system is operative in the basolateral membrane of the cat salivary epithelium. The properties of this system appear to be similar to the system y+ which has been described in several other cell types.