Cytochrome c activates K+ channels before inducing apoptosis.
Cell shrinkage is an early prerequisite for apoptosis. The apoptotic volume decrease is due primarily to loss of cytoplasmic ions. Increased outward K+ currents have indeed been implicated in the early stage of apoptosis in many cell types. We found that cytoplasmic dialysis of cytochrome c (cyt-c), a mitochondria-dependent apoptotic inducer, increases K+ currents before inducing nuclear condensation and breakage in pulmonary vascular smooth muscle cells. The cyt-c-mediated increase in K+ currents took place rapidly and was not affected by treatment with a specific inhibitor of caspase-9. Cytoplasmic dialysis of recombinant (active) caspase-9 negligibly affected the K+ currents. Furthermore, treatment of the cells with staurosporine (ST), an apoptosis inducer that mediates translocation of cyt-c from mitochondria to the cytosol, also increased K+ currents, caused cell shrinkage, and induced apoptosis (determined by apoptotic nuclear morphology and TdT-UTP nick end labeling assay). The staurosporine-induced increase in K+ currents concurred to the volume decrease but preceded the activation of apoptosis (nuclear condensation and breakage). These results suggest that the cyt-c-induced activation of K+ channels and the resultant K+ loss play an important role in initiating the apoptotic volume decrease when cells undergo apoptosis.
Platoshyn
Oleksandr
O
Department of Medicine, UCSD Medical Center, University of California-San Diego, 200 W Arbor Drive, San Diego, CA 92103-8382, USA.
Zhang
Shen
S
McDaniel
Sharon S
SS
Yuan
Jason X-J
JX
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism / Q000494:pharmacology; D048429:Cell Size / Q000187:drug effects; D002478:Cells, Cultured; D003574:Cytochrome c Group / Q000378:metabolism / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020287:In Situ Nick-End Labeling; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D017551:Microdialysis; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D011651:Pulmonary Artery; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D019311:Staurosporine / Q000494:pharmacology
D061945:Caspase Inhibitors; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D015221:Potassium Channels; D011994:Recombinant Proteins; C506435:Casp9 protein, rat; D053453:Caspase 9; D020169:Caspases; D019311:Staurosporine; D011188:Potassium