Influence of extracellular pH on the viability and morphology of tumor cells exposed to hyperthermia.

The influence of hyperthermia (42.5 degrees C) on the viability and morphology of L1A2 ascites cells incubated at various pH levels (6.4-7.2) was studied. In contrast to unheated cells, increased extracellular acidity in hyperthermically treated tumor cells was associated with markedly reduced viability of the tumor cells exposed to hyperthermia. The cells heated at neutral pH underwent ultrastructural nuclear changes; the most prominent were the appearance of filamentous bundles and increased perichromatin granules. The cells heated under more acid conditions had an increased lysosomal activity and intense cell lysis resulting in lethal damage to the entire cell population within 6 hours after treatment. The active mechanism was not clear, but cell membrane lesions combined with the increased lysosome activity seemed of major importance in the mechanism of heat-induced damage to tumor cells kept in an acid milieu.