Fundamental Ca2+ signaling mechanisms in mouse dendritic cells: CRAC is the major Ca2+ entry pathway

Although Ca2+-signaling processes are thought to underlie many dendritic ce ll (DC) functions, the Ca2+ entry pathway's are unknown. Therefore, we inve stigated Ca2+-signaling in mouse myeloid DC using Ca2+ imaging and electrop hysiological techniques. Neither Ca2+ currents nor changes in intracellular Ca2+ were detected following membrane depolarization, ruling out the prese nce of functional voltage-dependent Ca2+ channels. ATP, a purinergic recept or ligand, and 1-4 dihydropyridines, previously suggested to activate a pla sma membrane Ca2+ channel in human myeloid DC, both elicited Ca2+ rises in murine DC. However, in this study these responses were found to be due to m obilization from intracellular stores rather than by Ca2+ entry. In contras t, Ca2+ influx was activated by depletion of intracellular Ca2+ stores with thapsigargin, or inositol trisphosphate. This Ca2+ influx was enhanced by membrane hyperpolarization, inhibited by SKIT 96365, and exhibited a cation permeability similar to the Ca2+ release-activated Ca2+ channel (CRAG) fou nd in T lymphocytes. Furthermore, ATP, a putative DC chemotactic and matura tion factor, induced a delayed Ca2+ entry with a voltage dependence similar to CRAC. Moreover, the level of phenotypic DC maturation was correlated wi th the extracellular Ca2+ concentration and enhanced by thapsigargin treatm ent. These results suggest that CRAC is a major pathway for Ca2+ entry in m ouse myeloid DC and support the proposal that CRAC participates in DC matur ation and migration.