Sodium pump activity and contractile effect of ouabain in human placental veins.
The aim of the present study was to determine the number and affinity of [3H]ouabain binding sites, the sodium pump activity and the mechanisms involved in the contractile effects of ouabain in human placental veins. Scatchard analysis suggested the existence of a single population of binding sites with a KD of 196.7 nM and a Bmax of 1606 fmol/mg protein. The sodium pump activity was determined from the 86Rb+ uptake, which was reduced concentration dependently by ouabain (10(-8)-10(-4) M), and from the K+ (7.5 mM)-induced relaxation in veins preincubated in a K(+)-free medium and precontracted with PGF2 alpha (10(-6) M), which was also blocked by the glycoside (10(-6) M). Ouabain (10(-7)-10(-4) M) induced concentration-dependent contractions, which were not modified by either nifedipine or Bay K 8644 (10(-7) and 10(-6) M). Ca2+ omission from the medium or amiloride (10(-4) M) inhibited these contractions, whereas monensin (10(-6) M) potentiated them. These data indicate that human placental veins possess sodium pump activity and that its inhibition by ouabain induces potent contractions mainly mediated by Ca2+ entry through the Na(+)-Ca2+ exchange system.
Marín
J
J
Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma, Madrid, Spain.
Fernández-Alfonso
M S
MS
Sánchez-Ferrer
C F
CF
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D001665:Binding Sites; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism; D015237:Dinoprost / Q000494:pharmacology; D006801:Humans; D008985:Monensin / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D009543:Nifedipine / Q000494:pharmacology; D010042:Ouabain / Q000378:metabolism / Q000494:pharmacology*; D010920:Placenta / Q000098:blood supply*; D011188:Potassium / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D014680:Veins / Q000187:drug effects / Q000378:metabolism / Q000502:physiology
D010042:Ouabain; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D000584:Amiloride; D008985:Monensin; D015237:Dinoprost; D000254:Sodium-Potassium-Exchanging ATPase; D009543:Nifedipine; D012413:Rubidium; D011188:Potassium; D002118:Calcium