Temperature dependency of calcium responses in mammary tumour cells

Changes of intracellular calcium concentration ([Ca2+]i) induced by 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 microM) and bradykinin (0.1 nM-1 microM) induced the increase of [Ca2+]i at both temperatures and Ca(2+)-depletion did not affect these [Ca2+]i responses. Both [Ca2+]i responses became more sensitive at 35 degrees C than at 24 degrees C. A clear latency of [Ca2+]i increase after the application of the agonists was observed, and it changed with the concentration of the agonist. As concentrations of ATP or bradykinin became lower, the latency and rise time became longer. At higher concentrations, the latency and rise time approached a constant value. The latency shortened remarkably at 35 degrees C. These results suggested the involvement of a regenerative or threshold process in the [Ca2+]i responses in mammary tumour cells.