Inversion of the intracellular Na+/K+ ratio blocks apoptosis in vascular smooth muscle at a site upstream of caspase-3.
Long term elevation of the intracellular Na+/K+ ratio inhibits macromolecule synthesis and proliferation in the majority of cell types studied so far, including vascular smooth muscle cells (VSMC). We report here that inhibition of the Na+,K+ pump in VSMC by ouabain or a 1-h preincubation in K+-depleted medium attenuated apoptosis triggered by serum withdrawal, staurosporine, or okadaic acid. In the absence of ouabain, both DNA degradation and Caspase-3 activation in VSMC undergoing apoptosis were insensitive to modification of the extracellular Na+/K+ ratio as well as to hyperosmotic cell shrinkage. In contrast, protection of VSMC from apoptosis by ouabain was abolished under equimolar substitution of Na+o with K+o, showing that the antiapoptotic action of Na+,K+ pump inhibition was caused by inversion of the intracellular Na+/K+ ratio. Unlike VSMC, the same level of increment of the [Na+]i/[K+]i ratio caused by a 2-h preincubation of Jurkat cells with ouabain did not affect chromatin cleavage and Caspase-3 activity triggered by treatment with Fas ligand, staurosporine, or hyperosmotic shrinkage. Thus, our results show for the first time that similar to cell proliferation, maintenance of a physiologically low intracellular Na+/K+ ratio is required for progression of VSMC apoptosis.
Orlov
S N
SN
Centre de Recherche du Centre Hospitalier de l'Université de Montréal, Campus Hôtel-Dieu, University of Montreal, Montreal, Quebec, Canada.
Thorin-Trescases
N
N
Kotelevtsev
S V
SV
Tremblay
J
J
Hamet
P
P
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D048429:Cell Size; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D019169:Jurkat Cells; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism*
D004791:Enzyme Inhibitors; D010042:Ouabain; D012964:Sodium; D007770:L-Lactate Dehydrogenase; C505407:CASP3 protein, human; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D011188:Potassium