AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 2 369-R372, Copyright © 1991 by American Physiological Society
Sodium-dependent magnesium transport across in situ perfused rat placenta
A. J. Shaw, M. Z. Mughal, M. J. Maresh and C. P. Sibley
Department of Child Health, St. Mary's Hospital, University of Manchester, United Kingdom.
Placentas of anesthetized rats were perfused in situ on the fetal side to
study mechanisms of Mg2+ transport. The perfusate was a Mg(2+)-free
Krebs-Ringer, and the unidirectional transfer of Mg2+ from maternal plasma
to this Ringer was compared with that of 45Ca and 51Cr-EDTA, the latter
being employed as a paracellular diffusional marker. Placental perfusion
with amiloride (0.5 mM) or ouabain (1 mM) both rapidly (4 min) reduced
maternal-fetal clearance (Kmf) for Mg2+ but had no effect on Kmf for 45Ca.
In contrast, perfusion of the carbonic anhydrase inhibitor acetazolamide (1
mM) did not affect Kmf for Mg2+ or 45Ca. Placental perfusion with a
Na+-free Ringer reduced Kmf for both Mg2+ and 45Ca, although the latter
response was delayed. Kmf for 51Cr-EDTA was increased by amiloride and was
unaffected by perfusion of ouabain, acetazolamide, or Na+-free Ringer,
indicating that the effects of these treatments on Kmf of Mg2+ do not
reflect nonspecific effects on placental permeability. These data suggest
that maternal-fetal transfer of Mg2+ across the perfused rat placenta is
Na+ dependent.
