1. ¹Department of Bio-Materials Engineering and Cellular and Molecular Medicine, School of Medicine, Research Center for Proteineous Materials (RCPM), Chosun University, Gwangju, Korea
2. ²Department of Biology, Ewha Womans University, Seoul, Korea
3. ³Department of Biotechnology, Chosun University, Gwangju, Korea
4. ⁴Department of Chemistry and Medicinal Chemistry, Yonsei University, Wonju, Korea

Correspondence: I-S Park, Department of Bio-Materials Engineering and Cellular and Molecular Medicine, Research Center for Proteineous Materials (RCPM), School of Medicine, Chosun University, Gwangju 501-759, Korea. Tel: +8262 230 6753; Fax: +8262 227 8345; E-mail: parkis@chosun.ac.kr

⁵These authors contributed equally to this work.

Received 5 April 2007; Revised 13 July 2007; Accepted 26 July 2007; Published online 21 September 2007.

Abstract

Cellular ionic homeostasis, fundamentally K⁺ homeostasis, has been implicated as a critical regulator of apoptosis. The intracellular K⁺ efflux on apoptotic insult and suppression of apoptosis by high concentration of extracellular K⁺ or after inhibition of this efflux by K⁺ channel blockers have established the crucial role of K⁺ in turning on the apoptotic machinery. Several contrasting observations have reported the antiapoptotic effect of intracellular K⁺ concentration to be the result of inhibition of cytochrome c release from mitochondria, but the exact inhibitory mechanism remains obscure. However, here we show the blockage of K⁺ efflux during apoptosis did not affect cytochrome c release from the mitochondria, still completely inhibited the formation of the apoptosome comprising Apaf-1, cytochrome c, caspase-9 and other accessories. As a consequence of this event, procaspase-9, -3, -8 and other death-related proteins were not processed. Furthermore, physiological concentrations of K⁺ also inhibited the processing of procaspase-3 by purified caspase-8 or -9, the nucleosomal DNA fragmentation by purified DFF40/CAD and the nuclear fragmentation to varying extents. Altogether, these findings suggest that the efflux of K⁺ is prerequisite not only for the formation of the apoptosome but also for the downstream apoptotic signal-transduction pathways.