ENHANCEMENT OF CELL-KILLING AND INCREASE IN CYTOSOLIC CALCIUM-CONCENTRATION BY COMBINED TREATMENTS WITH HYPERTHERMIA AND TMB-8 IN MOUSE MAMMARY-CARCINOMA FM3A CELLS

Mouse mammary carcinoma FM3A cells were exposed 42-degrees-C or 44-degrees-C hyperthermia for 60 min in a culture medium with or without 8-(N,N-diethylamino) octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) at a concentration of 100 muM. Cell survival, cytosolic calcium ion concentration, [Ca2+]c, and influx of Ca-45(2+) were Investigated to examine the cardinal role of intracellular Ca2+ in hyperthermic cell killing. The [Ca2+]c in a single cell was measured by a digital image analyzing technique using Fura-2. TMB-8 enhanced cell killing, increase in [Ca2+]c, and influx of Ca-45(2+) induced by both hyperthermic treatments. In contrast, TMB-8 abolished the increase in [Ca2+]c induced by hyperthermia at 42-degrees-C and 44-degrees-C in the absence of extracellular Ca2+ . These results suggest that TMB-8, an agent usually called an inhibitor of intracellular calcium mobilization at 37-degrees-C or lower, enhances Ca2+ entry from the extracellular space at 42-degrees-C or 44-degrees-C and, in turn, promotes cell killing under hyperthermic conditions.