EFFECTS OF 42-DEGREES-C HYPERTHERMIA ON INTRACELLULAR PH IN OVARIAN-CARCINOMA CELLS DURING ACUTE OR CHRONIC EXPOSURE TO LOW EXTRACELLULAR PH

Purpose: To determine whether intracellular pH (pH(i)) is affected dur ing hyperthermia in substrate-attached cells and whether acute extrace llular acidification potentiates the cytotoxicity of hyperthermia via an effect on pH(i), Methods and Materials: The pH(i) was determined in cells attached to extracellular matrix proteins loaded with the fluor escent indicator dye BCECF at 37 degrees C and during 42 degrees C hyp erthermia at an extracellular pH (pH,) of 6.7 or 7.3 in cells, Effects on pH(i) during hyperthermia are compared to effects on clonogenic su rvival after hyperthermia at pH(e), 7.3 and 6.7 of cells grown at pH, 7.3, or of cells grown and monitored at pH, 6.7, Results: The results show that pH(i) values are affected by substrate attachments, Cells at tached to extracellular matrix proteins had better signal stability, l ow dye leakage and evidence of homeostatic regulation of pH(i) during heating, The net decrease in pH(i) in cells grown and assayed at pH(e) = 7.3 during 42 degrees C hyperthermia was 0.28 units and the decreas e in low pH adapted cells heated at pH(e), = 6.7 was 0.14 units, Acute acidification from pH(e), = 7.3 to pH, = 6.7 at 37 degrees C caused a n initial reduction of 0.5-0.8 unit in pH(i), but a partial recovery f ollowed during the next 60-90 min, Concurrent 42 degrees C hyperthermi a caused the same initial reduction in pH(i) in acutely acidified cell s, but inhibited the partial recovery that occurred during the next 60 -90 min at 37 degrees C, After 4 h at 37 degrees C, the net change in pH(i) in acutely acidified cells was 0.30 pH unit, but at 42 degrees C is 0.63 pH units, The net change in pH(i) correlated inversely with c lonogenic survival. Conclusions: Hyperthermia causes a pH(i) reduction in cells which was smaller in magnitude by 50% in low pH adapted cell s, Hyperthermia inhibited the partial recovery from acute acidificatio n that was observed at 37 degrees C in substrate attached cells, in pa rallel with a lower subsequent clonogenic survival, (C) 1997 Elsevier Science Inc.