Na⁺ deprivation induces persistent cell shrinkage and apoptotic cell death

Abstract

Although cell shrinkage is one of the phenotypical features of apoptosis, it has been controversial whether it is a prerequisite to apoptosis induction. In this study, we examined whether a persistent decrease in cell volume could per se initiate apoptotic cell death without any apoptotic stimulus. When HeLa cells were incubated in isotonic Na⁺-free solution, the mean cell volume immediately began to decrease and reached 84% of the original value within 30 min. After persistent shrinkage, activation of caspase-3 and reduction of cell viability were observed. Application of a blocker of the Na⁺-K⁺-2Cl⁻ cotransporter (NKCC), bumetanide (100 μM) or furosemide (1 mM), or that of the Na⁺/Ca²⁺ exchanger (NCX), KB-R7943 (25 μM), inhibited Na⁺ deprivation-induced shrinkage and attenuated apoptotic cell death. These results suggest that shrinkage of HeLa cells exposed to Na⁺-free solution is induced by efflux of Na⁺, K⁺ and Cl⁻ mediated by operation of NKCC and reversed operation of NCX, and that an isotonic volume decrease per se triggers the apoptotic process. [J Physiol Sci. 2006;56 Suppl:S118]