The restriction of calcium influx in metaphase and post‐metaphase stages of cell division revealed by imaging secondary ion mass spectrometry (SIMS).

A secondary ion mass spectrometry (SIMS)‐based isotopic imaging technique of ion microscopy was used for observing calcium influx in single renal epithelial LLC‐PK1 cells. The CAMECA IMS‐3f SIMS instrument, used in the study, is capable of producing isotopic images of single cells at 500 nm spatial resolution. Due to the high‐vacuum requirements of the instrument the cells were prepared cryogenically with a freeze‐fracture method and frozen freeze‐dried cells were used for SIMS analysis. The influx of calcium was imaged directly by exposure of cells to 44Ca stable isotope in the extracellular buffer for 10 min. The 44Ca influx was measured at mass 44 and the distribution of endogenous calcium at mass 40 (40Ca) in the same cell. A direct comparison of interphase cells to cells undergoing division revealed that calcium influx is restricted in metaphase and post‐metaphase stages of cell division. This restriction is lifted in late cytokinesis. The net influx of 44Ca in 10 min was approximately half under calcium influx restriction in comparison to interphase cells. Under calcium influx restriction the 44Ca concentration was the same between the mitotic chromosome and the cytoplasm. These observations indicate that the endoplasmic reticulum (ER) calcium uptake is compromised under calcium influx restriction in cells undergoing division. LAY DESCRIPTION: A mass spectrometry‐based isotopic imaging technique of ion microscopy was used to study the influx of calcium in cells undergoing division. The cells growing in culture were exposed to extracellular nutrient medium made from 44Ca stable isotope for 10 min. The 44Ca influx in interphase and dividing cells was imaged directly with ion microscopy. A comparison of interphase to dividing cells revealed that cells in metaphase and post‐metaphase stages restrict 44Ca influx. This restriction continued through cytokinesis and is lifted in late cytokinesis stage when the daughter cells are barely attached. Physiological implications of such restriction are still to be studied and may include protection of dividing cells from harmful calcium waves. [ABSTRACT FROM AUTHOR]