NA-ATPASE OF HUMAN PLACENTA DURING GESTATIONAL HYPERTENSION - A BIOCHEMICAL-BIOPHYSICAL STUDY(,K+)

1. Na+,K+-ATPase is the membrane enzyme catalysing the active transpor t of Na+ and K+ across the plasma membrane of animal cells, A reduced activity of Na+,K+-ATPase has been described in gestational hypertensi on in a variety of cell types, in agreement with the hypothesis that g estational hypertension can induce membrane transport modifications si milar to those reported for essential hypertension, The causes of the reduced Na+,K+-ATPase activity are still debated. 2. The aim of the pr esent work was to investigate the molecular mechanism of the reduced e nzymic activity in gestational hypertension using as a model Na+,K+-AT Pase purified from human placenta. Na+,K+-ATPase obtained from term pl acentas of eight healthy pregnant women and eight age-matched women wi th gestational hypertension was purified as previously described. 3. W e observed in gestational hypertension: (i) a significant increase in the activation energies above transition temperature; (ii) a significa nt decrease in the fluorescence polarization of (4-trimethylaminopheny l)-6-phenyl-1,3,5-hexatriene (i,e, increased fluidity) and an increase in the mean lifetime (modified hydrophobicity); (iii) a lower K-q, su ggesting an enzymic structural modification; and (iv) an increased mea n lifetime and rotational relaxation time of pyrene isothiocyanate, in dicating a modified ATP binding site.