Inhibition of K+ efflux prevents mitochondrial dysfunction and suppresses constitutive apoptosis in human neutrophils

Abstract

Circulating human neutrophils (PMN) die rapidly and their survival is contingent upon rescue from programmed cell death by signals from the inflammatory environment. Diminution of cell volume during apoptosis is closely linked to loss of intracellular K+. We investigated whether prevention of K+ efflux could affect the constitutively active apoptotic machinery. Culture of isolated human PMN in media containing KCl (10–120 mM) attenuated K+ efflux, suppressed apoptosis (assessed by annexin V binding and nuclear DNA content) and prolonged survival within 24–48 h of culture. KCl did not evoke phosphorylation of ERK and Akt, nor did inhibitors of these pathways render PMN insensitive to the anti-apoptotic actions of KCl. Inhibition of K+ efflux effectively attenuated collapse in mitochondrial transmembrane potential and mitochondrial cytochrome c release, resulting in decreased caspase-3 activity. Co-treatment of PMN with KCl and the pan-caspase inhibitor Z-VAD-FMK (20 μM) resulted in slightly greater suppression of apoptosis than KCL alone, suggesting the involvement of mechanism(s) other than inhibition of caspase-3. Our results indicate that inhibition of K+ efflux promote PMN survival by suppressing apoptosis through preventing mitochondrial dysfunction independent of ERK and phosphatidylinositol 3-kinase. Thus, K+ released locally from damaged cells may function as a survival signal for PMN, leading to amplification of neutrophil-mediated tissue injury (Supported by CIHR).