Cytotoxic hyperthermia and Ca2+ homeostasis: the effect of heat on Ca2+ uptake by nonmitochondrial intracellular Ca2+ stores.
The effect of cytotoxic hyperthermia on Ca2+ transport by intracellular, nonmitochondrial Ca2+ stores of the human colon cancer cell line, HT-29, was studied using cells permeabilized with saponin. Saponin treatment permitted equilibration of the cytosol with a defined extracellular medium consisting of an intracellular-like ionic composition, ATP and an ATP-regenerating system, and Ca2+/EGTA buffers to adjust the free [Ca2+]. Under the conditions employed, ATP-dependent Ca2+ uptake in saponin-permeabilized cells was demonstrated to be exclusively due to nonmitochondrial Ca2+ stores, e.g., endoplasmic reticulum or calciosomes. Heat treatment for 120 min at 44.5 degrees C sufficient to kill 80% of the cells inhibited ATP-dependent Ca2+ uptake by 50% in terms of rate and total Ca2+ accumulated. With cells made thermotolerant by either arsenite or heat treatment 24 h prior to challenge heating, ATP-dependent Ca2+ uptake was resistant to a second equivalent heat dose. Efflux of Ca2+ from saponin-permeabilized cells when measured at 37 degrees C was unaffected by a prior heat treatment (44.5 degrees C for 120 min).
Mikkelsen
R B
RB
Department of Radiation Oncology, Medical College of Virginia, Richmond 23298-0058.
Stedman
T
T
D000255:Adenosine Triphosphate / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003110:Colonic Neoplasms / Q000473:pathology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006706:Homeostasis / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D014407:Tumor Cells, Cultured / Q000378:metabolism*
D000255:Adenosine Triphosphate; D002118:Calcium