AJP - Cell Physiology, Vol 258, Issue 3 C443-C451, Copyright © 1990 by American Physiological Society
Taurine transport by microvillous membrane vesicles and the perfused cotyledon of the human placenta
P. I. Karl and S. E. Fisher
Department of Pediatrics, North Shore University Hospital-Cornell University Medical College, Manhasset, New York 11030.
Human placental uptake and maternal-to-fetal (M-to-F) net transfer of
taurine were evaluated in purified microvillous membrane vesicles (MMV) and
the isolated perfused cotyledon. Taurine uptake by MMV was specifically
stimulated by an inward Na+ gradient [maximum velocity (Vmax), 24.5 +/- 0.6
pmol.mg-1.30 s-1; Michaelis constant (Km), 6.2 +/- 0.7 microM], with uptake
stoichiometry showing approximately 2 Na+/taurine molecule. In the presence
or absence of Na+, Cl- did not stimulate uptake. Na(+)-stimulated uptake
was enhanced by an outward K+ gradient. beta-Alanine and hypotaurine
competitively inhibited uptake of taurine in MMV. Two-way uptake inhibition
studies showed no interaction between taurine and non-beta-amino acids.
When MMV were preloaded with taurine there was enhancement of
Na(+)-stimulated uptake. In the perfused placentas, saturable M-to-F net
transfer of taurine was not observed, despite saturation of tissue uptake
from the maternal circulation. During 3 h of perfusion, no
fetal-to-maternal (F-to-M) gradient formed for taurine; yet, a 2:1 gradient
simultaneously occurred for histidine. This study demonstrates that taurine
uptake by the microvillous membrane of the human placenta is highly
specific, of high affinity, and Na+ coupled.
