Intracellular Ca 2+ distribution and its dynamics are essential for various cellular functions. We show with single HeLa cells that a microscopic heat pulse induces Ca 2+ uptake into intracellular stores during heating and Ca 2+ release from them at the onset of recooling, and the overshoot of Ca 2+ release occurs above the critical value of a temperature change, which decreases from 1.5 to 0.2 °C on increasing the experimental temperature from 22 to 37 °C. This highly thermosensitive Ca 2+ dynamics is probably attributable to the altered balance between Ca 2+ uptake by endoplasmic reticulum Ca 2+-ATPases and Ca 2+ release via inositol 1,4,5-trisphosphate receptors. These results suggest that Ca 2+ signaling is extremely sensitive to temperature changes, especially around body temperature, in cells expressing inositol 1,4,5-trisphosphate receptors.
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