Glycine transport in human erythrocytes.

Abstract

SUMMARY1. Glycine transport in human erythrocytes was resolved into five separate components of uptake. The first and major component of uptake was transport by a high-affinity (apparent Km 25/tM) Na+-and Cl--dependent system. This system was specific for glycine, sarcosine and proline; Br-but not I-was able to substitute for Cl-. Uptake by this route was inhibited < 20 % by the loop diuretics, bumetanide and furosemide (10-4M), suggesting that it was distinct from the Cl--dependent system responsible for Na+/K+ transport. Its properties closely resembled those of the gly transport system described previously in avian erythrocytes.2. The second uptake route was transport by the Na+-dependent, Cl--independent small neutral amino acid transport system (designated ASC). Neither Na+-dependent uptake route was present in sheep erythrocytes.3. Two Na+-independent uptake mechanisms were also identified; first, uptake by the amino acid transport system (designated L), and secondly, SITS-sensitive uptake by the anion-exchange (band 3) transport mechanism (SITS is 4-acetamido-4'-iso-thiocyanatostilbene-2,2'-disulphonic acid, an effective ihibitor of anion transport by this route). Uptake by the latter route was increased markedly when fluxes were measured in isotonic SO42-medium or when the pH was increased.4. At 0-2 mm extracellular glycine, the relative contributions of each of these uptake routes to the total glycine flux were 42, 11, 15 and 160% for the gly, ASC, L and band 3 systems, respectively. 5. Finally, there was a residual Na+-independent component of glycine uptake which contributed 160 of the total flux. With the exception of the gly system, all uptake routes showed a linear concentration dependence up to 2 mM-glycine.

The effect of a hyposmotic shock on amino acid efflux from lactating rat mammary tissue: stimulation of taurine and glycine efflux via a pathway distinct from anion exchange and volume‐activated anion channels

“…In addition we found that niflumic acid, a high-affinity inhibitor of anion exchange in red cells (Cousin & Motais, 1979), attenuated the volume-activated efflux of taurine. Although a small portion of taurine exists as an anion at physiological pH and glycine has been shown to be a substrate of the human red cell anion-exchange system (Ellory, Jones & Young, 1981) there are several lines of evidence to suggest that the DIDS-sensitive component of taurine (and glycine) efflux from mammary tissue is not mediated via an exchange system. First, the magnitude of the volume-sensitive taurine efflux was not increased by the presence of taurine in the incubation medium.…”

Mammary-tissue amino acid transport systems

“…The notion that amino acids can utilize the anion exchanger is not new; Ellory et al (1981) found that glycine, under isosmotic conditions, is a substrate of the erythrocyte anion exchanger. However, the observation that the transport of sulfate, a substrate of the anion exchanger in mammary tissue (Shennan, 1989), is unaffected by cell swelling suggests that volume-activated amino acid efflux from rat mammary tissue does not use the anionexchange mechanism (Shennan et al 1994~2).…”

The role of anion transport in the passive movement of lead across the human red cell membrane.

“…The anion-transport system can bring about the net movement of anions, but it has been suggested that this occurs by 'tunneling' of the anion, rather than exchange of the anion with an unloaded site (Knauf, Law & Marchant, 1983;Frdhlich, 1984). Glycine can be carried by the red cell anion system (Ellory, Jones & Young, 1981). It is not known if the transported species is the zwitterion, or one of the charged forms.…”