Hypertonic Saline Attenuates Colonic Tumor Cell Metastatic Potential by Activating Transmembrane Sodium Conductance Conor J. Shields 1 , Desmond C. Winter 1 , John P. Geibel 2,3 , Gerald C. OÕSullivan 1 , Jiang Huai Wang 1 , H. Paul Redmond 1 1 Department of Surgery, National University of Ireland, Cork, Ireland 2 Department of Surgery, Yale University, New Haven, Connecticut, USA 3 Department of Cellular and Molecular Physiology, Yale University, New Haven, Connecticut, USA Received: 6 February 2006/Revised: 24 April 2006 Abstract. Hypertonic saline (HTS) suppresses tumor cell-endothelial interactions by reducing integrin expression. This translates into reduced adhesion, migration and metastatic potential. This study determined the relative contributions of hyperosmo- larity and sodium-specific hypertonicity on the inhibitory effects of HTS, the intracellular pH and sodium responses to HTS and the role of cytoskeletal remodeling in these changes. Human colonic tumor cells (LS174T) were exposed to lipopolysaccharide under isotonic, hypertonic, sodium-free (N-methyl- D-glucamine), hyperosmolar (mannitol or urea), disrupted cytoskeletal (10 lg/ml cytochalasin D) conditions or in the presence of 5-(N-ethyl-N-iso- propyl)amiloride (EIPA). b 1 integrin expression was measured flow-cytometrically. Intracellular sodium and pH were measured with confocal laser micro- scopic imaging. Statistical analysis was performed with analysis of variance, and P < 0.05 was consid- ered significant. Data are represented as mean ± - SEM. Hypertonic exposure attenuated integrin expression (62.03 ± 4.7% of control, P < 0.04). No discernible effect was observed with sodium-free or hyperosmolar solutions. HTS evoked a cellular alkalinization (by a mean 0.2 pH units) and an in- crease in cytosolic sodium concentration (by a mean 12.4 mM, P < 0.001) via upregulation of sodium- hydrogen exchange. Disassembly of actin microfila- ments by cytochalasin D and antiporter inhibition with EIPA abrogated the effect of hypertonicity on integrin expression and intracellular sodium and pH (P < 0.05). HTS downregulates adhesion mole- cule expression via a hypertonic, sodium-specific, cytoskeletally mediated mechanism that involves activation of sodium-hydrogen exchange with associated changes in intracellular pH and sodium concentrations. Key words: Hypertonic saline — Colonic tumor cell — Metastasis — Transmembrane sodium conductance Introduction Refined fluid and electrolyte balance is a pivotal component of modern surgical care, where hyper- tonic fluids exert beneficial cardiovascular, renal, pulmonary, gastrointestinal and immunomodulatory effects (Deb et al., 1999; Andrews et al., 2001; Umenishi, Narikiyo & Schrier, 2004; Shao et al., 2005; Toung et al., 2005). The propensity for hyper- tonic fluids to alter host responses to sepsis and inflammation has rekindled interest in them as resuscitative agents (Shields et al., 2003a, 2003b; Powers et al., 2005). In particular, HTS decreases neutrophil potency, an effect attributed to perturba- tion of adhesion molecule expression (Ciesla et al., 2001; Shields et al., 2003a, 2003b). However, it remains unknown whether the effects of hypertonic saline (HTS) are due to hyperosmolarity-induced cell shrinkage or electrochemical (ionic tonicity) influ- ences on cellular processes. Rizoli, Rotstein and Kapus (1999) suggested that cell volume changes are central by demonstrating shedding of L-selectin from neutrophils under hypertonic conditions derived from both sodium chloride and sucrose. However, it is challenging to separate one from the other; Thiel et al., (2001) postulated that reduced cell volume is not sufficient to account for the inhibitory effect on leukocyte integrin upregulation. Correspondence to: C. Shields; email: conor@narrowpoint.com J. Membrane Biol. 211, 35–42 (2006) DOI: 10.1007/s00232-006-0011-8