Mechanism of calcium oscillations in migrating human astrocytoma cells

Numerous studies show that intracellular calcium controls the migration rat e of different mobile cell types. We studied migrating astrocytoma cells fr om two human cell lines, U-87MG and A172, in order to clarify the mechanism s by which calcium potentially influences cell migration. Using the wound-h ealing model to assay migration, we showed that four distinct components of migration could be distinguished: (i) a Ca2+/serum-dependent process; (ii) a Ca2+-dependent/serum-independent process; (iii) a Ca2+/serum-independent process; (iv) a Ca2+-independent/serum-dependent process. In U-87MG cells which lack a Ca2+-dependent/serum-independent component, we found that intr acellular Ca2+ oscillations are involved in Ca2+-dependent migration. Remov ing extracellular Ca2+ greatly decreased the frequency of migration-associa ted Ca2+ oscillations. Furthermore, non-selective inhibition of Ca2+ channe ls by heavy metals such as Cd2+ or La3+ almost completely abolished changes in intracellular Ca2+ observed during migration, indicating an essential r ole for Ca2+ channels in the generation of these Ca2+ oscillations. However , specific blockers of voltage-gated Ca2+ channels, including nitrendipine, omega -conotoxin GVIA, omega -conotoxin MVIIC or low concentrations of Ni2 + were without effect on Ca2+ oscillations. We examined the role of interna l Ca2+ stores, showing that thapsigargin-sensitive Ca2+ stores and InsP(3) receptors are involved in. Ca2+ oscillations, unlike ryanodine-sensitive Ca 2+ stores. Detailed analysis of the spatio-temporal aspect of the Ca2+ osci llations revealed the existence of Ca2+ waves initiated at the leading cell edge which propagate throughout the cell. Previously, we have shown that t he frequency of Ca2+ oscillations was reduced in the presence of inhibitory antibodies directed against beta3 integrin subunits. A simple model of a C a2+ oscillator is proposed, which may explain how the generation of Ca2+ os cillations is linked to cell migration. (C) 2000 Elsevier Science B.V. All rights reserved.