Mechanism of calcium oscillations in migrating human astrocytoma cells

Numerous studies show that intracellular calcium controls the migration rate of different mobile cell types. We studied migrating astrocytoma cells from two human cell lines, U-87MG and A172, in order to clarify the mechanisms by which calcium potentially influences cell migration. Using the wound-healing model to assay migration, we showed that four distinct components of migration could be distinguished: (i) a Ca(2+)/serum-dependent process; (ii) a Ca(2+)-dependent/serum-independent process; (iii) a Ca(2+)/serum-independent process; (iv) a Ca(2+)-independent/serum-dependent process. In U-87MG cells which lack a Ca(2+)-dependent/serum-independent component, we found that intracellular Ca(2+) oscillations are involved in Ca(2+)-dependent migration. Removing extracellular Ca(2+) greatly decreased the frequency of migration-associated Ca(2+) oscillations. Furthermore, non-selective inhibition of Ca(2+) channels by heavy metals such as Cd(2+) or La(3+) almost completely abolished changes in intracellular Ca(2+) observed during migration, indicating an essential role for Ca(2+) channels in the generation of these Ca(2+) oscillations. However, specific blockers of voltage-gated Ca(2+) channels, including nitrendipine, omega-conotoxin GVIA, omega-conotoxin MVIIC or low concentrations of Ni(2+) were without effect on Ca(2+) oscillations. We examined the role of internal Ca(2+) stores, showing that thapsigargin-sensitive Ca(2+) stores and InsP(3) receptors are involved in Ca(2+) oscillations, unlike ryanodine-sensitive Ca(2+) stores. Detailed analysis of the spatio-temporal aspect of the Ca(2+) oscillations revealed the existence of Ca(2+) waves initiated at the leading cell edge which propagate throughout the cell. Previously, we have shown that the frequency of Ca(2+) oscillations was reduced in the presence of inhibitory antibodies directed against beta3 integrin subunits. A simple model of a Ca(2+) oscillator is proposed, which may explain how the generation of Ca(2+) oscillations is linked to cell migration.