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 cell (DC) functions, the Ca²⁺ entry pathways are unknown. Therefore, we investigated Ca²⁺-signaling in mouse myeloid DC using Ca²⁺ imaging and electrophysiological techniques. Neither Ca²⁺ currents nor changes in intracellular Ca²⁺ were detected following membrane depolarization, ruling out the presence of functional voltage-dependent Ca²⁺ channels. ATP, a purinergic receptor ligand, and 1-4 dihydropyridines, previously suggested to activate a plasma 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 mobilization from intracellular stores rather than by Ca²⁺ entry. In contrast, Ca²⁺ influx was activated by depletion of intracellular Ca²⁺ stores with thapsigargin, or inositoi trisphosphate. This Ca²⁺ influx was enhanced by membrane hyperpolarization, inhibited by SKF 96365, and exhibited a cation permeability similar to the Ca²⁺ release-activated Ca²⁺ channel (CRAC) found in T lymphocytes. Furthermore, ATP, a putative DC chemotactic and maturation factor, induced a delayed Ca²⁺ entry with a voltage dependence similar to CRAC. Moreover, the level of phenotypic DC maturation was correlated with the extracellular Ca²⁺ concentration and enhanced by thapsigargin treatment. These results suggest that CRAC is a major pathway for Ca²⁺ entry in mouse myeloid DC and support the proposal that CRAC participates in DC maturation and migration.