Furosemide, a Blocker of Na+/K+/2Cl− Cotransporter, Diminishes Proliferation of Poorly Differentiated Human Gastric Cancer Cells by Affecting G0/G1 State

PHARMACOLOGICAL TREATMENTS FOR TINNITUS: NEW AND OLD

Subjective tinnitus, the phantom ringing or buzzing sensation that occurs in the absence of sound, affects 12-14% of adults; in some cases the tinnitus is so severe or disabling that patients seek medical treatment. However, although the economic and emotional impact of tinnitus is large, there are currently no FDA-approved drugs to treat this condition. Clinical trials are now underway to evaluate the efficacy of N-methyl-d-aspartate (NMDA) and dopamine D(2) antagonists, selective serotonin reuptake inhibitors (SSRIs), γ-aminobutyric acid (GABA) agonists and zinc dietary supplements. Previous off-label clinical studies, while not definitive, suggest that patients with severe depression may experience improvement in their tinnitus after treatment with antidepressants such as nortriptyline or sertraline. A small subpopulation of patients with what has been described as "typewriter tinnitus" have been shown to gain significant relief from the anticonvulsant carbamazepine. Preliminary studies with misoprostol, a synthetic prostaglandin E1 analogue, and sulpiride, a dopamine D(2) antagonist, have shown promise. Animal behavioral studies suggest that GABA transaminase inhibitors and potassium channel modulators can suppress tinnitus. Additionally, improvements in tinnitus have also been noted in patients taking melatonin for significant sleep disturbances. Like other complex neurological disorders, one drug is unlikely to resolve tinnitus in all patients; therapies targeting specific subgroups are likely to yield the greatest success.

Chloride ions control the G1/S cell-cycle checkpoint by regulating the expression of p21 through a p53-independent pathway in human gastric cancer cells

The aim of the present study is to investigate whether the chloride affects cell growth and cell-cycle progression of cancer cells. In human gastric cancer MKN28 cells, the culture in the Cl(-)-replaced medium (replacement of Cl(-) by NO(3)(-)) decreased the intracellular chloride concentration ([Cl(-)](i)) and inhibited cell growth. The inhibition of cell growth was due to cell-cycle arrest at the G(0)/G(1) phase caused by diminution of CDK2 and phosphorylated Rb. The culture of cells in the Cl(-)-replaced medium significantly increased expressions of p21 mRNA and protein without any effects on p53. These observations indicate that chloride ions play important roles in cell-cycle progression by regulating the expression of p21 through a p53-independent pathway in human gastric cancer cells, leading to a novel, unique therapeutic strategy for gastric cancer treatment via control of [Cl(-)](i).

[Cl-]i modulation of Ca2+-regulated exocytosis in ACh-stimulated antral mucous cells of guinea pig

The effects of intracellular Cl- concentration ([Cl-]i) on acetylcholine (ACh)-stimulated exocytosis were studied in guinea pig antral mucous cells by video microscopy. ACh activated Ca2+-regulated exocytosis (an initial phase followed by a sustained phase). Bumetanide (20 microM) or a Cl- -free (NO3-) solution enhanced it; in contrast, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB, a Cl- channel blocker) decreased it and eliminated the enhancement induced by bumetanide or NO3- solution. ACh and Ca2+ dose-response studies demonstrated that NO3- solution does not shift their dose-response curves, and ATP depletion studies by dinitrophenol or anoxia demonstrated that exposure of NO3- solution prior to ATP depletion induced an enhanced initial phase followed by a sustained phase, whereas exposure of NO3- solution after ATP depletion induced only a sustained phase. Intracellular Ca2+ concentration ([Ca2+]i) measurements showed that bumetanide and NO3- solution enhanced the ACh-stimulated [Ca2+]i increase. Measurements of [Cl-]i revealed that ACh decreases [Cl-]i and that bumetanide and NO3- solution decreased [Cl-]i and enhanced the ACh-evoked [Cl-]i decrease; in contrast, NPPB increased [Cl-]i and inhibited the [Cl-]i decrease induced by ACh, bumetanide, or NO3- solution. These suggest that [Cl-]i modulates [Ca2+]i increase and ATP-dependent priming. In conclusion, a decrease in [Cl-]i accelerates ATP-dependent priming and [Ca2+]i increase, which enhance Ca2+-regulated exocytosis in ACh-stimulated antral mucous cells.

Chloride-dependent acceleration of cell cycle via modulation of Rb and cdc2 in osteoblastic cells

In the present study, we investigated if Cl(-) regulates the proliferation of the MC3T3-E1 osteoblastic cells. The proliferation of MC3T3-E1 osteoblastic cells was diminished by lowering the extracellular Cl(-) concentration ([Cl(-)](o)) in the culture medium. The lowered in [Cl(-)](o) increased the periods of the G(0)/G(1) and the G(2)/M phases in cell cycle. We further studied the effects of [Cl(-)](o) on the key enzymes, Rb and cdc2, playing key roles in checking points of the G(0)/G(1) and the G(2)/M phases in cell cycle. The lowered in [Cl(-)](o) diminished the active forms of enzymes, Rb and cdc2. We further found that the action of lowered [Cl(-)](o) on the cell proliferation, the cell cycle, Rb and cdc2 was abolished by the presence of 2mM glutamine, but not by that of pyruvate as another Krebs cycle substrate. Taken together, these observations indicate here for the first time that Cl(-) modulates Rb and cdc2, enhancing the proliferation of the MC3T3-E1 osteoblastic cells.

Essential role of NKCC1 in NGF-induced neurite outgrowth

The Na(+)/K(+)/2Cl(-) cotransporter (NKCC) mediates electroneutral transport of 2Cl(-) coupled with Na(+) and K(+) across the plasma membrane, and plays crucial roles in Cl(-) uptake into the cells, homeostasis of cellular Cl(-), and cell volume regulation. However, we have very limited information on the roles of ion transporters in neurite outgrowth in neuronal cells. In the present study, we report the role of NKCC1 (an isoform of NKCC) in NGF-induced neurite outgrowth of rat pheochromocytoma PC12D cells. The expression level of NKCC1 protein was increased by NGF treatment. Knock-down of NKCC1 by RNA interference (RNAi) drastically diminished the NGF-induced neurite outgrowth. Transfection of enhanced green fluorescent protein (EGFP)-tagged rat NKCC1 into cells for clarification of intracellular localization of NKCC1 revealed that the EGFP-rNKCC1 was mainly localized in the plasma membrane at growth cone during neurite outgrowth. These observations suggest that NKCC1 plays a fundamental role in NGF-induced neurite outgrowth of PC12D cells.