Ouabain, a steroid hormone that signals with slow calcium oscillations.
The plant-derived steroid, digoxin, a specific inhibitor of Na,K-ATPase, has been used for centuries in the treatment of heart disease. Recent studies demonstrate the presence of a digoxin analog, ouabain, in mammalian tissue, but its biological role has not been elucidated. Here, we show in renal epithelial cells that ouabain, in doses causing only partial Na,K-ATPase inhibition, acts as a biological inducer of regular, low-frequency intracellular calcium ([Ca(2+)](i)) oscillations that elicit activation of the transcription factor, NF-kappa B. Partial inhibition of Na,K-ATPase using low extracellular K(+) and depolarization of cells did not have these effects. Incubation of cells in Ca(2+)-free media, inhibition of voltage-gated calcium channels, inositol triphosphate receptor antagonism, and redistribution of actin to a thick layer adjacent to the plasma membrane abolished [Ca(2+)](i) oscillations, indicating that they were caused by a concerted action of inositol triphosphate receptors and capacitative calcium entry via plasma membrane channels. Blockade of ouabain-induced [Ca(2+)](i) oscillations prevented activation of NF-kappa B. The results demonstrate a new mechanism for steroid signaling via plasma membrane receptors and underline a novel role for the steroid hormone, ouabain, as a physiological inducer of [Ca(2+)](i) oscillations involved in transcriptional regulation in mammalian cells.
Aizman
O
O
Department of Woman and Child Health, Karolinska Institutet, Astrid Lindgren Children's Hospital, Q2:09, S-171 76 Stockholm, Sweden.
Uhlén
P
P
Lal
M
M
Brismar
H
H
Aperia
A
A
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D007150:Immunohistochemistry; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D008297:Male; D018613:Microscopy, Confocal; D016328:NF-kappa B / Q000378:metabolism; D010042:Ouabain / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013347:Subcellular Fractions / Q000378:metabolism
D016328:NF-kappa B; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium