The effects of urinary digitalislike factor on cultured vascular smooth muscle cells.Hypertension

SUMMARY We attempted to purify a digitalislike factor from human urine. On the assumption that a natural ligand for the digitalis receptor should be searched for on the basis of the effects on intact cells, we used an inhibitory effect on the binding of [3H]ouabain to human erythrocytes to determine digitalislike activity. A highly polar [3H]ouabain displacing activity was obtained by a combination of chromatographic procedures including reverse-phase high performance liquid chro-matography. Urine-derived pHJouabain displacing activity, a competitive inhibitor of ouabain bind-ing to human erythrocytes, acted on human lymphocytes in a similar manner. The dose-response curve of this compound was parallel to that of ouabain. Urine-derived [3H]ouabain displacing activity significantly inhibited monensin-stimulated increase in ouabain-sensitive MRb uptake, a parameter of Na+,K+-adenosine triphosphatase (ATPase), by 95 % (p<0.01) in cultured vascular smooth muscle cells (A10 cells). Furthermore, this compound enhanced net **Ca influx by 30 % (p<0.01) and reduced ^Ca efflux by 35 % (p<0.01) in A10 cells. These results suggest that urine-derived [3H]oua-bain displacing activity may be a regulator of Na+,K+-ATPase and a modulator of vascular tone. (Hypertension 11: 645-650, 1988) KEY WORDS * hypertension * Na +,K+-adenosine triphosphatase inhibitor • rubidium-8