Figure 5.

Downregulation of the volume-regulated Cl⁻ current/taurine release pathway in multi-drug resistant (MDR) Ehrlich ascites cells (EATC) and elimination of cisplatin-induced apoptosis following addition of the Cl⁻ channel blocker NS3728. (a) The volume-activated Cl⁻ current was measured using a whole-cell patch-clamp technique following hypotonic exposure (reduction of the extracellular medium to two-third of the isotonic value). (b) Volume-activated release of the organic osmolyte taurine was estimated as the maximal obtainable rate constant following hypotonic exposure. The MDR value is relative to the value in Wt cells. (c) Caspase 3 activity was measured using a calorimetric assay to detect production of p-nitroanilide by cleavage of the substrate acetyl-Asp-Glu-Val-Asp p-nitroanilide. NS3728 was added to block the Cl⁻ current, and the free concentration of NS3728 was determined using Centrifree YM-30 micropartition devices and ¹⁴C-labelled NS3728. In (a,b), asterisk (*) indicates significant differences compared with Wt EATC. In (c), asterisk (*) indicates a significant difference compared with control cells without cisplatin, and plus symbol (+) indicates a significant difference between Wt and MDR EATC cells. Adapted from [19].