Inhibitor action on placental calcium transport

Summary

Human term placental lobules were dually perfused with Krebs Ringer solution at 37°C under open circuit conditions. Provided that perfusate Ca²⁺ concentrations were between 2.33 and 2.55 mM, there was a steady release of Ca²⁺ into the fetal circulation and uptake of Ca²⁺ from the maternal circulation. There was no significant calcium (Ca) protein binding in the perfusates. Addition of dinitrophenol altered the release of Ca²⁺ to an uptake on the fetal circuit and enhanced Ca²⁺ uptake on the maternal circuit. It also produced a release of potassium (K)⁺ and an uptake of Na⁺ on both sides of the placenta. Ouabain had no significant effect on Ca movements although it produced a marked release of K⁺ into the fetal perfusate. The effect of cooling on the fetal circuit was similar to that of dinitrophenol (DNP), although it did not produce significant changes in either Ca²⁺ or K⁺ movements on the maternal side of the lobule. Both DNP and cooling reduced the Ca concentration ratio between fetal and maternal outflows to unity. Replacement of Na⁺ by choline Ringer had only transient effect on the extraction of⁴⁵Ca from fetal perfusate. These observations indicate that a Ca²⁺/Na (sodium)⁺ exchanger does not make a major contribution to the transplacental movement of Ca²⁺ from mother to fetus and that this process is more probably associated with membrane-bound ATPases.