Cellular mechanisms of action of a ouabain-like factor in vascular smooth-muscle cells.
Ouabain-like factor (OLF) has been implicated to play an important role in certain forms of hypertension. We isolated OLF from the urine of salt-loaded healthy subjects by stepwise chromatographic procedures. The post-salt fraction (F IV) eluted from Sephadex G-25 was rechromatographed on Sephadex G-10. A late small-molecular-weight fraction F8 inhibited Na-K-ATPase in vitro (OLF activity). The effects of OLF on intracellular Ca2+ concentrations ([Ca2+]i) and pH (pHi) were examined in cultures of vascular smooth-muscle cells using the fluorescent probes fura-2 and 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF), respectively. Preincubation with OLF increased basal [Ca2+]i from 87 +/- 6 to 160 +/- 8 nM (p < 0.001) and enhanced arginine vasopressin-stimulated maximal [Ca2+]i (418 +/- 11 vs. 523 +/- 14 nM, p < 0.01). This effect was similar to that of ouabain. OLF also induced a rapid transient increase of [Ca2+]i (82 +/- 9 vs. 253 +/- 23 nM, p < 0.01); [Ca2+]i returned to levels slightly above baseline within approximately 4 min. OLF-stimulated [Ca2+]i was attenuated by verapamil (126 +/- 5 nM, p < 0.01) and was also reduced in Ca(2+)-free medium (104 +/- 9 nM, p < 0.01). As opposed to OLF, ouabain did not exhibit this fast transient effect on [Ca2+]i. Amiloride (10(-3) M) blocked the sustained effect of OLF on [Ca2+]i (77 +/- 11 vs. 86 +/- 12 nM, NS). OLF induced an increase of pHi from 7.09 +/- 0.03 to 7.28 +/- 0.04 (p < 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)
Meyer-Lehnert
H
H
Medizinische Universitäts-Poliklinik, University of Bonn, Germany.
Wanning
C
C
Michel
H
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Bäcker
A
A
Kramer
H J
HJ
D000328:Adult; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism; D001127:Arginine Vasopressin / Q000494:pharmacology; D001685:Biological Factors / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002298:Cardenolides; D002478:Cells, Cultured; D004077:Digoxin; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008970:Molecular Weight; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012503:Saponins; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D001685:Biological Factors; D002298:Cardenolides; D012503:Saponins; C034504:digoxin-like factors; D001127:Arginine Vasopressin; D010042:Ouabain; D004077:Digoxin; D000584:Amiloride; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium