The magnesium, calcium, sodium, potassium and chloride contents of the term human placenta.

The ion content of the human term placenta was determined. When ordered decreasingly according to their placental content, the series of ions was: Na greater than Cl greater than K greater than Ca greater than Mg. These levels, plotted as a function of the tissue dry weight, showed an exponential distribution. Using Cl as an extracellular marker, Na and K cellular concentrations were evaluated. The equilibrium potentials derived from these values were very different from the measured syncytial membrane potential or from the value usually recorded in non-innervated tissues.