Nuclear and cytosolic calcium signaling induced by extracellular ATP in rat kidney inner medullary collecting duct cells.

Using a laser scanning confocal microscopy of fluorescent Ca2+ indicator (Fluo-3-AM) the spatiotemporal Ca2+ dynamics in cultured kidney inner medullary collecting duct cells was investigated. In response to extracellular ATP (100 microM), nuclear (Fln) and cytosolic (Flc) fluorescence intensity increased simultaneously. UTP similarly increased Fln and Flc, but ADP and AMP did not. A ratio between Fln and Flc was about 1.06 +/- 0.03 at rest and increased 1.71 +/- 0.02 at the peak of stimulation (n = 74). In Ca(2+)-free condition, ATP increased Fln and Flc with a smaller peak intensity, but the peak ratio was similar (1.52 +/- 0.03, n = 70). Faster time resolution of 100 ms in line scanning mode did not detect the delay between nuclear and cytosolic Ca2- responses. Our results indicate that nuclear Ca2+ was not diffused from the cytoplasm and that it may be directly released from the nuclear envelope, a possible Ca2+ store.