Influence of heat on Na-dependent HC function in a thermoresistant cell line +-O Cl exchanger 3

Abstract

During previous studies on the relationship between thermosensitivity and intracellular pH (pHi) regulation in mammalian cells, we observed that the thermoresistant TR-4 cells appeared to be resistant to manipulations of the Na+ H+ antiport, one of the two primary membrane regulators of pHi. We hypothesized that this might be due to up-regulation of the alternate pHi regulator,the Na+-dependent HCO3/Cl-exchanger, in the TR-4 cells. We have now evaluated the effect of heat exposure on the function of the Na+-dependent HCO3 /Cl-exchanger in both the parent RIF-1 and the thermoresistant variant TR-4 cells. We also assessed thermosensitivity of the cell lines under conditions of either pH 7.2 or 6.8, with NaHCO, with or without the addition of e 3- DIDS, an inhibitor of HCO /Cl exchanger function. After 3 2h of heating at 43 C, relative exchanger function declined to around 50 for the TR-4 cells and 10 for the RIF-1 cells. DIDS (0.2 mM) enhanced thermal cytotoxicity in both cells lines, by around 1 log when the cells were heated at neutral conditions, and by around 1.5log when the condition became acidic. Results from pH measurements during heati ing reflected the clonogenic survival data in that lower pHi levels were associated with the conditions when DIDS was present. We conclude that in the TR-4 cells, the Na+-dependent HCO3/Cl exchanger appears to be a more important regulator of pHi than the Na+ H+ antiport.