THE RELATIONSHIP BETWEEN INTRACELLULAR PH AND HEAT SENSITIVITY IN A THERMORESISTANT CELL-LINE

To explore further the relationship between intracellular pH (pH(i)) a nd thermosensitivity, we compared survival and pH(i) levels in RIF-1 c ells and a thermoresistant variant, TR-4 cells, while heating under di fferent conditions of acid or neutral extracellular pH (pH(e)). We als o added 5-(N-ethyl-N-isopropyl) amiloride (EIPA), a potent inhibitor o f one of the major membrane regulators of pH(i), the NA(+)/H+ antiport , and/or removed NaHCO3 to inactivate the alternate membrane regulator of pH(i), the HCO3-/Cl- exchanger. At pH(e) 7.3 with 7.3 with NaHCO3, EIPA (15 mu M) did not enhance the cytoxicity of heat in either cell line. At pH(e) 6.8 with NaHCO3, EIPA enhanced thermal cytotoxicity for RIF-1 cells only, but without NAHCO(3), at pH(3) 6.8 or 6.5, EIPA tre atment during heating resulted in a significant decrease in survival o f TR-4 cells also. Measurements of pH(i) levels immediately after heat ing correlated with the survival data, demonstrating a linear relation ship between pH(i) and log surviving fraction for both cell lines. Thi s relationship, however, is different between the two cell lines in th at the TR-4 cells are more resistant to reduction in pH(i) with heatin g, and for any given pH(i) level demonstrate a higher surviving fracti on compared to the RIF-1 cells. In addition, this correlation is diffe rent for the two cell line, suggesting a difference in the relationshi p between pH(i) and log surviving fraction between the TR-4 and RIF-1 cells. (C) 1996 by Radiation Research Society.