Thermosensitization and modification of cytosolic calcium concentration by verapamil and diltiazem in mouse mammary carcinoma cells.
OBJECTIVE
The cardinal role of Ca2+ signaling in the development of heat damage at 42 degrees C and 44 degrees C and the effect of verapamil and diltiazem on the change of cytosolic Ca2+ concentration, [Ca2+]c, were investigated.


METHODS
Hyperthermic treatment was performed by immersing the tubes containing the mouse mammary carcinoma FM3A cells in a water-bath set at 42.0 degrees C or 44.0 degrees C. The [Ca2+]c of a single cell after hyperthermia was monitored by a digital image analyzing technique using Fura-2. Influx of Ca2+ was examined by the measurement of the radioactivity of 45Ca2+ incorporated into the cells for 60 min during or after hyperthermia.


RESULTS
While the [Ca2+]c of the cells treated at 37 degrees C for 60 min was less than 230 nM, the percentage of the cells showing more than 230 nM increased after 42 degrees C hyperthermia and that of the cells showing more than 300 nM increased after 44 degrees C hyperthermia. When cellular uptake of 45Ca2+ during and after hyperthermia was examined, the increase in 45Ca2+ uptake was observed only for 44 degrees C hyperthermia. Verapamil or diltiazem (100 microM) enhanced a delay of cell growth, an increase in [Ca2+]c and an increase in 45Ca2+ influx for 42 degrees C and 44 degrees C hyperthermia.


CONCLUSIONS
These results are compatible with the view that the increase in [Ca2+]c after 42 degrees C hyperthermia results from intracellular release from calcium store sites whereas the rise in [Ca2+]c after 44 degrees C hyperthermia is mainly due to entry of extracellular Ca2+. Verapamil or diltiazem combined with hyperthermia increased [Ca2+]c, which may play a cardinal role in thermosensitization by these agents.
Kondo
T
T
Department of Radiation Biophysics, Kobe University School of Medicine, Japan.
Habara
Y
Y
Kanno
T
T
Kano
E
E
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004110:Diltiazem / Q000494:pharmacology*; D006358:Hot Temperature; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology*
D014700:Verapamil; D004110:Diltiazem; D002118:Calcium