Phospholipase C-β1 and β4 Contribute to Non-Genetic Cell-to-Cell Variability in Histamine-Induced Calcium Signals in HeLa Cells

A uniform extracellular stimulus triggers cell-specific patterns of Ca2+ signals, even in genetically identical cell populations. However, the underlying mechanism that generates the cell-to-cell variability remains unknown. We monitored cytosolic inositol 1,4,5-trisphosphate (IP3) concentration changes using a fluorescent IP3 sensor in single HeLa cells showing different patterns of histamine-induced Ca2+ oscillations in terms of the time constant of Ca2+ spike amplitude decay and the Ca2+ oscillation frequency. HeLa cells stimulated with histamine exhibited a considerable variation in the temporal pattern of Ca2+ signals and we found that there were cell-specific IP3 dynamics depending on the patterns of Ca2+ signals. RT-PCR and western blot analyses showed that phospholipase C (PLC)-beta 1, -beta 3, -beta 4, -gamma 1, -delta 3 and -epsilon were expressed at relatively high levels in HeLa cells. Small interfering RNA-mediated silencing of PLC isozymes revealed that PLC-beta 1 and PLC-beta 4 were specifically involved in the histamine-induced IP3 increases in HeLa cells. Modulation of IP3 dynamics by knockdown or overexpression of the isozymes PLC-beta 1 and PLC-beta 4 resulted in specific changes in the characteristics of Ca2+ oscillations, such as the time constant of the temporal changes in the Ca2+ spike amplitude and the Ca2+ oscillation frequency, within the range of the cell-to-cell variability found in wild-type cell populations. These findings indicate that the heterogeneity in the process of IP3 production, rather than IP3-induced Ca2+ release, can cause cell-to-cell variability in the patterns of Ca2+ signals and that PLC-beta 1 and PLC-beta 4 contribute to generate cell-specific Ca2+ signals evoked by G protein-coupled receptor stimulation.