Modulation of Ca2+ Signaling by Na+/Ca2+ Exchangers in Mast Cells

Abstract

Mast cells rely on Ca(2+) signaling to initiate activation programs leading to release of proinflammatory mediators. The interplay between Ca(2+) release from internal stores and Ca(2+) entry through store-operated Ca(2+) channels has been extensively studied. Using rat basophilic leukemia (RBL) mast cells and murine bone marrow-derived mast cells, we examine the role of Na(+)/Ca(2+) exchangers. Calcium imaging experiments and patch clamp current recordings revealed both K(+)-independent and K(+)-dependent components of Na(+)/Ca(2+) exchange. Northern blot analysis indicated the predominant expression of the K(+)-dependent sodium-calcium exchanger NCKX3. Transcripts of the exchangers NCX3 and NCKX1 were additionally detected in RBL cells with RT-PCR. The Ca(2+) clearance via Na(+)/Ca(2+) exchange represented approximately 50% of the total clearance when Ca(2+) signals reached levels > or =200 nM. Ca(2+) signaling and store-operated Ca(2+) entry were strongly reduced by inverting the direction of Na(+)/Ca(2+) exchange, indicating that Na(+)/Ca(2+) exchangers normally extrude Ca(2+) ions from cytosol and prevent the Ca(2+)-dependent inactivation of store-operated Ca(2+) channels. Working in the Ca(2+) efflux mode, Na(+)/Ca(2+) exchangers such as NCKX3 and NCX3 might, therefore, play a role in the Ag-induced mast cell activation by controlling the sustained phase of Ca(2+) mobilization.