Elevated extracellular [K+] inhibits death-receptor- and chemical-mediated apoptosis prior to caspase activation and cytochrome c release

• Published in: Biochemical journal 2001-07, Vol.357 (Pt 1), p.137-145
• Main Authors: Thompson, G J, Langlais, C, Cain, K, Conley, E C, Cohen, G M
• Format: Article
• Language: English
• Subjects: Amino Acid Chloromethyl Ketones - pharmacology; Antibodies - pharmacology; Apoptosis - drug effects; Apoptosis - physiology; Caspase Inhibitors; Caspases - metabolism; Cysteine Proteinase Inhibitors - pharmacology; Cytochrome c Group - metabolism; Cytosol - physiology; Enzyme Activation; Etoposide - pharmacology; Extracellular Space - physiology; fas Receptor - drug effects; fas Receptor - physiology; Flow Cytometry; Humans; Intracellular Membranes - drug effects; Intracellular Membranes - physiology; Jurkat Cells; Kinetics; Membrane Potentials - physiology; Mitochondria - drug effects; Mitochondria - physiology; Phosphatidylserines - metabolism; Potassium - pharmacology; Potassium Chloride - pharmacology; Receptors, Tumor Necrosis Factor - drug effects; Receptors, Tumor Necrosis Factor - physiology; Rubidium - pharmacokinetics; T-Lymphocytes - cytology; T-Lymphocytes - drug effects; T-Lymphocytes - physiology; Tumor Cells, Cultured
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/0264-6021:3570137

Efflux of intracellular K(+) and cell shrinkage are features of apoptosis in many experimental systems, and a regulatory role has been proposed for cytoplasmic [K(+)] in initiating apoptosis. We have investigated this in both death-receptor-mediated and chemical-induced apoptosis. Using Jurkat T cells pre-loaded with the K(+) ion surrogate (86)Rb(+), we have demonstrated an efflux of intracellular K(+) during apoptosis that was concomitant with, but did not precede, other apoptotic changes, including phosphatidylserine externalization, mitochondrial depolarization and cell shrinkage. To further clarify the role of K(+) ions in apoptosis, cytoprotection by elevated extracellular [K(+)] was studied. Induction of apoptosis by diverse death-receptor and chemical stimuli in two cell lines was inhibited prior to phosphatidylserine externalization, mitochondrial depolarization, cytochrome c release and caspase activation. Using a cell-free system, we have demonstrated a novel mechanism by which increasing [K(+)] inhibited caspase activation. In control dATP-activated lysates, Apaf-1 oligomerized to a biologically active caspase processing approximately 700 kDa complex and an inactive approximately 1.4 MDa complex. Increasing [K(+)] inhibited caspase activation by preventing formation of the approximately 700 kDa complex, but not of the inactive complex. Thus intracellular and extracellular [K(+)] markedly affect caspase activation and the initiation of apoptosis induced by both death-receptor ligation and chemical stress.