Morphological changes in L1210 leukaemic cells induced by hyperthermia

The colonogenic survival of L1210 leukaemic cells was assessed by spleen colony assay after cells were heated for 5, 10, 15 or 30 minutes at 43 degrees C. Similar cells which were fixed within 60 seconds of heating by glutaraldehyde were examined by scanning electron microscopy (SEM). The appearance of heated cells was compared with unheated controls which had been stored for one hour at 37 degrees C, 4 degrees C, and 22 degrees C respectively. After a heat treatment of 15 minutes at 43 degrees C the clonogenic fraction is only 0.1 but the appearance of approximately half the cells examined by SEM was unchanged. Virtually every cell heated for 30 minutes at 43 degrees C was abnormal. Progressive changes in the cell membrane were seen, such as loss of microvilli, folding and corrugation of the cell membrane and development of blebs. The lethal injury to cells is probably damage to enzyme systems in the cell membrane and elsewhere in the cell which is expressed as loss of clonogenicity. It is noteworthy that some cells appear to have been sterilised before morphological changes were seen. Two explanations are possible. The lethal injury as expressed by sterilisation may precede morphological changes or alternatively as cells had been heated for only a short time (10 or 15 minutes) and fixed within 60 seconds of heating, insufficient time had elapsed for gross changes to develop.