INFLUENCE OF ORGANIC CATIONS ON BASIC-AMINO-ACID UPTAKE BY HUMAN PLACENTAL VILLI

Human placental chorionic villi were incubated for 30 min with [H-3]ly sine or [H-3]arginine arid the distribution ratios (intracellular:extr acellular Concentrations) were determined. The ratios remained unchang ed when Na+ in Earle's buffered salt solution was replaced with Li+. W hen Na+ was replaced with choline there was a significant increase in distribution ratios (lysine 1.34 +/- 0.33 v. 3.99 + 0.15, arginine 1.9 5 +/- 0.37 v. 5.05 +/- 1.16). Leucine, a neutral amino acid with a Nat -independent transport system, was unaffected by choline substitution. The distribution ratio for alanine, which is Na+-dependent, was reduc ed (2.50 +/- 0.41 v. 1.45 +/- 0.20). Two other quarternary amines, ace tyl-beta-methylcholine and tetraethylammonium chloride (TEA) caused si milar increases in the distribution ratios of the basic amino acids. H ordenine, a tertiary amine, was less effective and there was little or no effect with ephedrine, a secondary amine. The choline effect was f irst observable at concentrations of 105 mM. With TEA, there was a pro gressive increase in distribution ratios beginning at 29 mM. Lysine ef flux was measured after incubation of villi with lysine in Earle's buf fer or choline buffer. Lysine was rapidly released to the fresh medium with 25% more retained in choline-exposed villi. The amines may cause alterations in the kinetics of basic amino-acid transporters or may m odify other aspects of placental physiology permitting an increased re tention of the basic amino acids.