title: The relationship between intracellular pH and heat sensitivity in a thermoresistant cell line.
abstract: To explore further the relationship between intracellular pH (pHi) and thermosensitivity, we compared survival and pHi levels in RIF-1 cells and a thermoresistant variant, TR-4 cells, while heating under different conditions of acid or neutral extracellular pH (pHe). We also added 5-(N-ethyl-N-isopropyl) amiloride (EIPA), a potent inhibitor of one of the major membrane regulators of pHi, the Na+/H+ antiport, and/or removed NaHCO3 to inactivate the alternate membrane regulator of pHi, the HCO3-/Cl- exchanger. At pHe 7.3 with NaHCO3, EIPA (15 microM) did not enhance the cytotoxicity of heat in either cell line. At pHe 6.8 with NaHCO3, EIPA enhanced thermal cytotoxicity for RIF-1 cells only, but without NaHCO3, at pHe 6.8 or 6.5, EIPA treatment during heating resulted in a significant decrease in survival of TR-4 cells also. Measurements of pHi levels immediately after heating correlated with the survival data, demonstrating a linear relationship between pHi and log surviving fraction for both cell lines. This relationship, however, is different between the two cell lines in that the TR-4 cells are more resistant to reduction in pHi with heating, and for any given pHi level to demonstrate a higher correlation is different for the two cell lines, suggesting a difference in the relationship between pHi and log surviving fraction between the TR-4 and RIF-1 cells.
authors.affiliation: Department of Radiation Oncology, Princess Margaret Hospital/Ontario Cancer Institute, Toronto, Canada.
authors.forename: F F
authors.initials: FF
authors.lastname: Liu
authors.forename: M D
authors.initials: MD
authors.lastname: Sherar
authors.forename: R P
authors.initials: RP
authors.lastname: Hill
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000502:physiology; D001639:Bicarbonates / Q000737:chemistry; D002460:Cell Line; D027963:Chloride-Bicarbonate Antiporters; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D051379:Mice; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors
chemical_list: D017920:Antiporters; D001639:Bicarbonates; D027963:Chloride-Bicarbonate Antiporters; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; C039614:ethylisopropylamiloride