Characterization of somatic Ca2+ clearance mechanisms in young and mature hippocampal granule cells.

Calcium is a key regulator for expression of genes relevant to survival and maturation of newborn neurons. Mammalian hippocampal dentate gyrus generates new granule cells (GCs) throughout adult life. We identified young and mature GCs in hippocampi of young adult mice according to their electrical properties, and investigated contributions of Na/Ca exchanger (NCX), sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA), plasma membrane Ca(2+)-ATPase (PMCA) and mitochondria to Ca(2+) clearance in somata of GCs. Somatic Ca(2+) clearance was increased by about 50% as GCs matured. NCX activity increased proportionally during maturation with its relative contribution kept about 40% both in young and mature GCs. On the other hand, the developmental increases in activities of mitochondria and SERCA resulted in higher contributions to Ca(2+) clearance in mature GCs than in young GCs. Especially mitochondrial function was most highly enhanced during maturation. PMCA activity, however, did not increase during maturation. Low Ca(2+) clearance in immature GCs might facilitate higher Ca(2+) accumulation during network activity, which in turn help survival of young GCs.