Search

The functions of chloride channels in preconditioning-induced cell protection remain unclear. In this report, we show that the volume-activated chloride channels play a key role in hydrogen peroxide (HO) preconditioning-induced cell protection in pheochromocytoma PC12 cells. The preconditioning with 100 μM HO for 90 min protected the cells from injury induced by long period exposure to 300 μM HO. The protective effect was attenuated by pretreatment with the chloride channel blockers, 5-nitro-2-3-phenylpropylamino benzoic acid (NPPB) and tamoxifen. HO preconditioning directly activated a chloride current, which was moderately outward-rectified and sensitive to the chloride channel blockers and hypertonicity-induced cell shrinkage. HO preconditioning functionally up-regulated the activities of volume-activated chloride channels and enhanced the regulatory volume decrease when exposure to extracellular hypotonic challenges. In addition, acute application of HO showed distinctive actions on cell volume and membrane permeability in HO preconditioned cells. In HO preconditioned cells, acute application of 300 μM HO first promptly induced a decrease of cell volume and enhancement of cell membrane permeability, and then, cell volume was maintained at a relatively stable level and the facilitation of membrane permeability was reduced. Conversely, in control cells, 300 μM HO induced a slow but persistent apoptotic volume decrease (AVD) and facilitation of membrane permeability. HO preconditioning also significantly up-regulated the expression of ClC-3 protein, the molecular candidate of the volume-activated chloride channel. These results suggest that HO preconditioning can enhance the expression and functional activities of volume-activated chloride channels, thereby modulate cell volume and cell membrane permeability, which may contribute to neuroprotection against oxidant-induced injury. [ABSTRACT FROM AUTHOR]

Chloride channels are expressed ubiquitously in different cells. However, the activation and roles of volume-activated chloride channels under normal isotonic conditions are not clarified, especially in lymphatic cells. In this study, the activation of basal and volume-activated chloride currents and their roles in maintenance of basal cell volume under isotonic conditions were investigated in human acute lymphoblastic leukemia Molt4 cells. The patch-clamp technique and time-lapse image analysis were employed to record whole-cell currents and cell volume changes. Under isotonic conditions, a basal chloride current was recorded. The current was weakly outward-rectified and volume-sensitive and was not inactivated obviously in the observation period. A 47% hypertonic bath solution and the chloride channel blockers NPPB and tamoxifen suppressed the current. Exposure of cells to 47% hypotonic bath solution activated further the basal current. The hypotonicity-activated current possessed properties similar to those of the basal current and was inhibited by NPPB, tamoxifen, ATP and hypertonic bath solution. Furthermore, extracellular hypotonic challenges swelled the cells and induced a regulatory volume decrease (RVD). Extracellular applications of NPPB, tamoxifen and ATP swelled the cells under isotonic conditions and inhibited the RVD induced by hypotonic cell swelling. The results suggest that some volume-activated chloride channels are activated under isotonic conditions, resulting in the appearance of the basal chloride current, which plays an important role in the maintenance of basal cell volume in lymphoblastic leukemia cells. Chloride channels can be activated further to induce a regulatory volume recovery when cells are swollen. [ABSTRACT FROM AUTHOR]