IngentaConnect L-Arginine Transport at the Fetal Side of Human Placenta: Effect ...

Authors: Acevedo C.G.¹; Rojas S.¹; Bravo I.¹

Source: Experimental Physiology, Volume 84, Number 6, November 1999 , pp. 1127-1136(10)

Abstract:

SUMMARY

l-Arginine transport by the fetal side of human placenta was investigated through the characterization ofl-[³H]arginine uptake in isolated perfused cotyledon. Competitive inhibition experiments suggest the presence of at least two transport systems: a Na⁺-independent, pH-insensitive system inhibitable by cationic amino acids, similar to system y⁺, and a Na⁺-dependent system which recognizes both cationic and neutral amino acids only in the presence of Na⁺, i.e. a B^o,+-like system. The kinetic analysis ofl-arginine uptake in the presence of Na⁺ revealed that the process is mediated by saturable components: a high-affinity system (K_m= 167 ± 18.0 mgr

M; V_max= 0.174 ± 0.012 mgr

mol min^-1) and a low-affinity carrier (K_m= 980 ± 112 mgr

M; V_max= 1.60 ± 0.12 mgr

mol min^-1). In the absence of Na⁺,l-arginine uptake was fitted by one model with a Michaelis-Menten constant of 200 ± 24.8 mgr

M. These results suggest that the high-affinity component corresponds to the Na⁺-independent system y⁺, whilst the low-affinity system may represent the activity of the Na⁺-dependent B^o,+ transporter. Kinetic studies in placentae taken from aspirin-treated pregnancies showed thatl-arginine is transported with a significantly higher affinity (K_m= 42.5 ± 5.7 mgr

M), but with a lower capacity (V_max= 0.064 ± 0.003 mgr

mol min^-1) than in the non-treated group. The latter finding suggests that aspirin would facilitate the uptake of the NO precursor only at very low arginine concentrations.

Document Type: Research article

DOI: 10.1111/j.1469-445X.1999.01875.x

Affiliations: 1: Department of Physiology Faculty of Biological Sciences, University of Concepción, PO Box 160-C, Concepción, Chile

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L-Arginine Transport at the Fetal Side of Human Placenta: Effect of Aspirin in Pregnancy