TEMPERATURE DEPENDENCY OF CALCIUM RESPONSES IN MAMMARY-TUMOR CELLS

Changes of intracellular calcium concentration ([Ca2(+)](i)) induced b y the extracellular application of ATP and bradykinin in mouse mammary tumour cells (MMT060562) were investigated by image analysis of fluo- 3 fluorescence at 24 degrees C and 35 degrees C. ATP (0.1-100 mu M) an d bradykinin (0.1 nM-1 mu M) induced the increase of[Ca2+](i) at both temperatures and Ca2+-depletion did not affect these [Ca2+](i) respons es. Both [Ca2+](i) responses became more sensitive at 35 degrees C tha n at 24 degrees C. A clear latency of [Ca2+](i) increase after the app lication of the agonists was observed, and it changed with the concent ration of the agonist. As concentrations of ATP or bradykinin became l ower, the latency and rise time became longer. At higher concentration s, the latency and rise time approached a constant value. The latency shortened remarkably at 35 degrees C. These results suggested the invo lvement of a regenerative or threshold process in the [Ca2+](i) respon ses in mammary tumour cells. (C) 1997 by John Wiley & Sons, Ltd.