Contribution of a H+ pump in determining the resting potential of neuroblastoma cells

Involvement of tumor acidification in brain cancer pathophysiology

Gliomas, primary brain cancers, are characterized by remarkable invasiveness and fast growth. While they share many qualities with other solid tumors, gliomas have developed special mechanisms to convert the cramped brain space and other limitations afforded by the privileged central nervous system into pathophysiological advantages. In this review we discuss gliomas and other primary brain cancers in the context of acid-base regulation and interstitial acidification; namely, how the altered proton (H⁺) content surrounding these brain tumors influences tumor development in both autocrine and paracrine manners. As proton movement is directly coupled to movement of other ions, pH serves as both a regulator of cell activity as well as an indirect readout of other cellular functions. In the case of brain tumors, these processes result in pathophysiology unique to the central nervous system. We will highlight what is known about pH-sensitive processes in brain tumors in addition to gleaning insight from other solid tumors.

K+ channel block-induced mammalian neuroblastoma cell swelling: a possible mechanism to influence proliferation

1. A variety of studies have suggested that K+ channel activity is a key determinant for cell progression through the G1 phase of mitosis. We have previously proposed that K+ channels control the activity of cell cycle-regulating proteins via regulation of cell volume. In order to test this hypothesis, we measured, with a Coulter counter and under different experimental conditions, the volume and rate of proliferation of neuroblastoma x glioma hybrid NG108-15 cells. 2. The K+ channel blockers TEA (1-10 mM), 4-aminopyridine (0.2-2 mM) and Cs+ (2.5-10 mM) increased the cell volume and decreased the rate of cell proliferation. Proliferation was fully inhibited when cell volume was increased by 25 %. 3. A 40 % increase in the culture medium osmolarity with NaCl induced a 25 % increase in cell volume and an 82 % decrease in the rate of cell proliferation. A 40 % increase in the culture medium osmolarity with mannitol induced a 9 % increase in cell volume and a 60 % decrease in the rate of cell proliferation. 4. The Cl- channel blocker NPPB (5-nitro-2-(3-phenylpropylamino) benzoic acid; 50 microM) induced a 12 % increase in cell volume and a 77 % decrease in the rate of cell proliferation. 5. A 24 % reduction in the culture medium osmolarity with H2O induced a 21 % decrease in cell volume and a 32 % increase in the rate of cell proliferation. 6. Under whole-cell patch-clamp conditions, antibiotics (penicillin plus streptomycin) decreased the voltage-dependent K+ current. Omission of antibiotics from the culture medium induced a 10 % decrease in the cell volume and a 32 % increase in the rate of cell proliferation. 7. These results suggest that the mechanisms controlling cell proliferation are strongly influenced by the factors which determine cell volume. This could take into account the role in mitogenesis of K+ channels and of other ionic pathways involved in cell volume regulation.