The role of intracellular Ca(2+) in apoptosis induced by hyperthermia and its enhancement by verapamil in U937 cells.
OBJECTIVE
The relationship between apoptosis induced by 42 degrees C and 44 degrees C hyperthermia alone or in combination with verapamil and changes in intracellular Ca(2+) concentration ([Ca(2+)]i) was investigated in U937 cells.


METHODS
Apoptosis induced by hyperthermia was assessed according to DNA fragmentation, nuclear morphologic changes, and expression of phosphatidylserine on the outside plasma cell membrane. These changes were measured by flow cytometry. The [Ca(2+)]i of individual cells after hyperthermia was monitored by a digital image-analyzing technique using Fura-2.


RESULTS
Hyperthermia-induced apoptosis reached a plateau after 6 h and was found to be both time and temperature-dependent. DNA fragmentation was maximum at 44 degrees C after 30 min. Verapamil enhanced the apoptosis induced by 42 degrees C and 44 degrees C hyperthermia in normal cells and by 44 degrees C hyperthermia in thermotolerant cells. The number of cells containing higher [Ca(2+)]i (more than 200 nM) was significantly increased by hyperthermia and further elevated by the addition of verapamil in both normal and thermotolerant cells. Apoptosis induced by hyperthermia was markedly decreased by an intracellular Ca(2+) chelator, BAPTA-AM, in a dose-dependent manner.


CONCLUSIONS
These results indicate that [Ca(2+)]i increase plays a crucial role in apoptosis induced by hyperthermia and the combined treatment with verapamil in normal and thermotolerant U937 cells. Furthermore, hyperthermia-combined drug therapy has potential significance in cancer therapy.
Kameda
K
K
Department of Radiology, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Toyama, Japan.
Kondo
T
T
Tanabe
K
K
Zhao
Q L
QL
Seto
H
H
D017209:Apoptosis / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D002614:Chelating Agents / Q000494:pharmacology; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D006979:Hyperthermia, Induced; D010718:Phosphatidylserines / Q000378:metabolism; D011853:Radiobiology; D013696:Temperature; D013997:Time Factors; D020298:U937 Cells / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D014700:Verapamil / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D002614:Chelating Agents; D010718:Phosphatidylserines; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D014700:Verapamil; D002118:Calcium