Monovalent ions control proliferation of Ehrlich Lettre ascites cells

Channels and transporters of monovalent ions are increasingly suggested as putative anticarcinogenic targets. However, the mechanisms involved in modulation of proliferation by monovalent ions are poorly understood. Here, we investigated the role of [K.sup.+], [Na.sup.+], and [Cl.sup.-] ions for the proliferation of Ehrlich Lettre ascites (ELA) cells. We measured the intracellular concentration of each ion in [G.sub.0], [G.sub.1], and S phases of the cell cycle following synchronization by serum starvation and release. We show that intracellular concentrations and content of [Na.sup.+] and [Cl.sup.-] were reduced in the [G.sub.0]-[G.sub.1] phase transition, followed by an increased content of both ions in S phase concomitant with water uptake. The effect of substituting extracellular monovalent ions was investigated by bromodeoxyuridine incorporation and showed marked reduction after [Na.sup.+] and [Cl.sup.-] substitution. In spectrofluorometric measurements with the pH-sensitive dye BCECF, substitution of [Na.sup.+] was observed to upregulate the activity of the [Na.sup.+]/[H.sup.+] exchanger NHE1 as well as of [Na.sup.+]-independent acid extrusion mechanisms, facilitating intracellular pH ([pH.sub.i]) recovery after acid loading and increasing [pH.sub.i]. Results using the potential sensitive dye [DiBaC.sub.4](3) showed a reduced [Cl.sup.-] conductance in S compared with [G.sub.1] followed by transmembrane potential ([E.sub.m]) hyperpolarization in S. [Cl.sup.-] substitution by impermeable anions strongly inhibited proliferation and increased free, intracellular [Ca.sup.2+] ([[[Ca.sup.2+]].sub.i]), whereas a more permeable anion had little effect. Western blots showed reduced chloride intracellular channel CLIC1 and chloride channel ClC-2 expression in the plasma membrane in S compared with [G.sub.1]. Our results suggest that [Na.sup.+] regulates ELA cell proliferation by regulating intracellular pH while [Cl.sup.-] may regulate proliferation by fine-tuning of [E.sub.m] in S phase and altered [Ca.sup.2+] signaling. cell cycle; chloride channel; volume regulatory anion channel; [Na.sup.+]/[H.sup.+] exchanger 1 doi: 10.1152/ajpcell.00445.2009.