ION MICROSCOPY EVIDENCE THAT LA3-COMPLEX IN LLC-PK1 CELLS( RELEASES CA2+ FROM GOLGI)

The effect of La3+ on LLC-PK1 cells was investigated by ion microscopy , a mass spectrometry-based technique with a spatial resolution of sim ilar to 0.5 mu m. Cells were incubated with LaCl3 for 10 min (1 mM) or 30 min (0.1 mM), and intracellular calcium distributions were measure d with a Cameca IMS-3f ion microscope in cryogenically prepared cells. Compared with control cells, La3+ reduced total calcium in the Golgi complex by > 100 mu M in both treatments, whereas other cellular regio ns, such as the nucleus and cytoplasm, remained largely unchanged. The se two treatments were repeated on cells that were preincubated with 1 mM ouabain. The presence of ouabain in the medium increased the loss of calcium from the Golgi by about fourfold compared with the treatmen ts without ouabain. The La3+ effect, therefore, was amplified by ouaba in-induced Na+ loading, indicating a possible involvement of a Na+/La3 + exchanger. La3+ was detected within cells and its influx was facilit ated by Na+ loading. These results suggest that La3+ may affect cellul ar calcium homeostasis by actions other than as a simple Ca2+ antagoni st.