MODIFICATIONS INDUCED BY PLASMA OF GESTATIONAL HYPERTENSIVE WOMEN ON THE NA+ K+-ATPASE OBTAINED FROM HUMAN PLACENTA/

In order to investigate the molecular mechanisms of the inhibition of Na+/K+-ATPase in Gestational Hypertension (GH), we incubated Na+/K+-AT Pase purified from human placenta of 6 healthy normotensive women with plasma from 6 GH women and 6 healthy controls. We determined the enzy me activity by the method of Esman, and the anthroyl-ouabain-binding c apacity, dissociation constant (K-d) and average lifetime values (tau) by the static and dynamic fluorescence of anthroyl-ouabain. The lipid annulus of the enzyme was studied by static and dynamic fluorescence of (4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). The a ddition of total and protein-free GH plasma to normal Na+/K+-ATPase si gnificantly inhibited the enzymatic activity even at the lowest concen tration studied (1:100), as well as the ouabain-binding capacity, K-d and tau. GH plasma significantly decreased the fluorescence polarizati on and lifetime values of TMA-DPH. These observations indicate that th e inhibition caused by GK plasma on Na+/K+-ATPase might be due to a re duction of the number of active molecules or a modification of the oua bain-binding site suggesting the existence of digitalis-like factor. A link between the modification of the lipid moiety of the enzyme and t he Na+/K+-ATPase inhibition might be hypothesized.